Dust and Ice: Their Roles in Astrophysical Environments

In view of the rich organic chemistry occurring in Titan’s atmosphere, the complicated reactions occurring on Titan’s surface material and the possible existence of a subsurface ocean, Titan may be the astrobiological hotspot in our solar system. Therefore, it is important to understand the chemical steps that lead to the formation of molecules with biological significance in this environment. Oxygen containing species are scarce in Titan’s atmosphere but present on the surface in the form of water-ice and metal‐oxide particles from meteorite impact. Organic molecules such as tholins, which consist mainly of nitrogen containing polyaromatic hydrocarbons, are also abundant on Titan’s surface. Since many molecules of biochemical interest contain oxygen (e.g., amino acids, sugars and nucleotides), evaluating the mechanistic pathways that can lead to the incorporation of oxygen into organics is essential to unraveling the mystery of the chemical evolution of life. Using low-energy electrons similar to those produced via the limited cosmic rays that penetrate Titan’s atmosphere and impact the surface, we have explored the reaction products formed from irradiation of water-organic ices on mineral substrates as an analog for Titan’s surface chemistry.

Many important molecules in astrochemistry are unstable or reactive species, and therefore difficult to study in the lab. Three such molecules are methoxymethanol (CH3OCH2OH), methanediol (HOCH2OH), and aminomethanol (NH2CH2OH). These molecules are predicted to form on grain surfaces in the initial steps of interstellar prebiotic molecular evolution. These molecules are thought to be precursors to complex molecules such as sugars and amino acids. To test these prebiotic interstellar chemical pathways, a pure rotational spectrum is required for comparison to interstellar line surveys. Given the reactivity and instability of these molecules under normal laboratory conditions, an efficient chemical formation mechanism is required before such laboratory studies can be conducted. O(1D) insertion reactions are one possible production route. O(1D) insertion reactions into C-H bonds are highly exothermic, and therefore highly efficient. We have constructed a supersonic expansion source which allows O(1D) to react with organic molecules on-the-fly, in the gas phase. The products are stabilized and isolated in the expansion, allowing spectroscopic study. We will present our experimental design and our progress toward obtaining high-resolution gas-phase spectra of these molecules.

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is now in its final development phase. The airplane is flying, the telescope assembly has been operated in flight, instruments are ready to go. First light observing and the first open call for proposals will both occur this spring. A revised Science Vision for SOFIA has been generated showing that the observatory will provide an important complement to the Herschel and JWST missions and as a platform for technology development. I will discuss the status of the observatory, highlight selected parts of the SOFIA Science Vision and preview some opportunities for community participation in both research and Education/Public Outreach with the observatory.

Cavity Ringdown Spectroscopy is an extremely sensitive high-resolution spectroscopic technique typically utilized in the visible and IR spectral windows.  Given its sensitivity, cavity ringdown is a useful technique for the detection and characterization of unstable or trace species. With the forthcoming Herschel, ALMA, and SOFIA observatories, high-resolution spectra of astrochemically-relevant molecules in the THz frequency range is necessary to interpret observed data. There are currently no high-resolution techniques with sufficient sensitivity in the frequency ranges of these observatories to enable characterization of most unstable molecules.  We are currently testing a high-reflectivity cavity formed from wire-grid polarizers for use in a continuous-wave cavity ringdown spectrometer in the THz range.  We plan to use this spectrometer to acquire spectra of trace and unstable species of astrochemical interest across the THz spectral window.   We will report on this instrument development and our plans to investigate reactive or unstable organic molecules that are important intermediates in interstellar chemistry.

Dust plays an indispensable role in the chemical evolution of protostellar regions from the catalytic production of molecular hydrogen to the formation of polyatomic species that are critical to the origins of life. We will discuss the sources of superthermal atoms in protostellar and circumstellar regions, and the ISM; then describe the JPL Facility for producing fast, ground-state H(2S) and O(3P) atoms of energy in the range 0.2-50 eV. Recent results will be given for production of CO2, H2CO, CH3OH, HCOOH, and CH3CH2OH. Species identification from temperature-programmed desorption mass spectra is made through a novel use of the Metropolis random-walk method. *(Presentation is with S. M. Madzunkov and J. A. MacAskill.)

The progenitors of planetary nebulae (PNe), asymptotic giant branch (AGB) stars, are considered the most efficient source of circumstellar dust in the Galaxy. However, it is not clear yet how much dust do PNe have and whether this dust is destroyed or modified during their lifetime. We study the dust present in a sample of 48 Galactic PNe through the analysis of their iron depletion factor, the ratio between the expected abundance of iron and the one measured in the gas phase. The derived depletion factors are consistently high in all the objects, suggesting that more than 80% of the iron atoms are condensed into dust grains. However, the depletions cover a wide range, with a difference in the iron abundance of a factor of ~100 for the objects with the highest and lowest values. The differences do not seem to be related to the age of the PNe, and we explore here the relation to the dust chemistry of the objects through their C/O abundance ratios and the dust features present in the available infrared spectra.

The gas phase infrared spectrum of protonated naphthalene is measured in a cold supersonic beam using mass-selected photodissociation spectroscopy and the messenger atom method. Sharp vibrational band structure is measured throughout the 800-3200 cm-1 region for comparison to the Unidentified Infrared Bands (UIRs). Protonated naphthalene exhibits strong bands at 3.5, 6.2, 7.7 and 8.6 μm that correspond to prominent UIR features. The 6.2 μm feature provides one of the first examples in laboratory spectra for an intense vibrational band at this wavelength. It arises from an "allyl-type" carbon ring distortion, which is a direct consequence of the perturbation on aromatic rings resulting from protonation in the σ configuration. The 3.5 and 7.7 μm features correspond to the stretches and scissors motion of the aliphatic CH2 group, which also follow directly from protonation. Other strong bands seen at 6.6 and 6.9 μm do not coincide with the strongest UIR features. Protonated naphthalene itself is not a perfect match for the UIR spectra, but it strongly suggests that larger H+PAH species are prominent among the UIR carriers.

Titanium carbide nanoclusters are produced in a molecular beam with pulsed laser vaporization. Mass spectra reveal the preferred stoichiometries present in these systems. Infrared spectra are measured for size-specific clusters using a free electron laser and the method of infrared multiphoton photoionization spectroscopy. Laboratory spectra for the nanocrystal species, which have cubic structures (rock salt lattice), match the previously unassigned 21 micron line found in post AGB spectra.

Gas-phase chemistry in the interstellar medium (ISM) can produce a host of important organic molecules including: simple sugars, amino acids, and nucleobases. These organics may condense onto icy grains where they undergo an additionally complex grain-chemistry which has a much wider range of synthesis products than does gas-phase chemistry. Species created in these environments are subject to concurrent destruction processes induced by the galactic cosmic radiation (GCR) and questions arise as to the equilibrium balance of these important biomolecules. UV photodestruction dominates in unshielded environments, but inside dense clouds or icy-grains the influence of energetic ion impact is significant. In this study, the degradation rate of the nucleobase adenine, in simulated icy-grain conditions, due to the MeV proton component of the GCR is measured. Destruction cross sections are obtained and half-lifetimes are calculated for astrobiologically relevant radiation environments. Comparison to reported UV destruction lifetimes is made and the possibility of extraterrestrial nucleobase delivery to the prebiotic Earth is discussed.

PAH emission has been observed in various astrophysical environments throughout our Galaxy and even in external galaxies. PAH emission is brightest in atomic regions; it is unknown whether this is due to the change in the abundance of PAHs, or is an excitation effect. Here we investigate whether PAHs exist only in the atomic region, or exist both in the atomic and molecular region, using two different models representing the Orion Nebula. Cases where PAHs are, or are not, in the molecular gas have similar PAH emission spectra, but the electron density in the molecular region is very different, which eventually affects the ion-molecular reactions. We further investigate which molecular species can be used to pin down one of the possibilities using observational data. HCO+ is an example of several molecules whose abundance depends inversely on the ambient electron density. Unfortunately, comparison with the available HCO+ and CS column density measurements in the Orion Bar does not clearly distinguish between these cases, but future, higher angular resolution observations can in principal do so.

Observations of ices in astrophysical environments are usually interpreted on the basis of the spectra of laboratory analogs. In this talk, we will present some astrophysical observations and discuss efforts in the laboratory to supply the spectra needed for interpretation. Specifically, I will discuss the IR absorption feature of interstellar solid carbon dioxide (CO2) as observed by the Spitzer Space Telescope and the vacuum-ultraviolet spectra of Saturnian satellites as observed by the Cassini UltraViolet Imaging Spectrograph (UVIS). I will also discuss new efforts spectroscopic techniques for interpreting ice features both in the near-infrared spectral region and in the far-infrared (or THz) spectral region.

We report preliminary results on sputtering of a lunar regolith simulant sample by H+, Ar+, Ar6+ and Ar9+ at solar wind-relevant energies. The ions are generated using an electron cyclotron resonance (ECR) ion source at source potentials between 10-15kV. After being extracted, transported, and decelerated, the ions are normally incident on a pressed lunar regolith stimulant sample that is situated within a floating UHV scattering chamber. The relative bias between the ECR source and the surface end station was adjusted to produce a constant impact energy of 0.375keV/amu for each of the 4 ion beams investigated. To simulate the effect of the dominant proton component, which constitutes >90% of the solar wind, the lunar regolith simulant sample was prepared by exposure to a proton beam up to total fluences of ~2x10^18 H+/cm2 prior to each of the Ar beam sputtering runs. Both transient and steady state conditions of sputtered species were monitored by a quadrupole mass spectrometer situated within the UHV scattering chamber. SEM and XPS analyses of the JSC-1A simulant were performed to monitor possible changes in surface morphology and composition during the pressing of the loose powder into the sample holder.

I discuss Gamma-Ray Burst (GRB) afterglow spectroscopy (X-ray and optical) as a means to study cosmic chemical evolution. The z(z) relation as probed with QSO-DLA and GRB-DLA systems implies some evidence for the expected cosmic abundance trends, but also reveals significant differences. Afterglow SEDs can also be used to infer the presence of dust, and since GRBs are known to exist at z > 8, the expected transition from SN-dominated dust to the present-day galactic mixtures can be probed.

Water is perhaps the most important and most pervasive chemical on our planet. The influence of water permeates virtually all areas of biochemical, chemical and physical importance, and is especially evident in phenomena occurring at the interfaces of solid surfaces. The water – metal oxide interaction is of particular importance in fields such as catalysis, electrochemistry, photoconversion, geochemistry, adhesion, sensors, atmospheric chemistry, and tribology. Researchers in these fields grapple with very basic questions regarding the interactions of water with oxide surfaces, such as how does water adsorb, what are the chemical and electrostatic forces that constitute the adsorbed layer, how is water thermally or non-thermally activated, and how do coadsorbates influence the properties of water. The attention paid to these and other fundamental questions has been immense in recent decades as experimental surface science methods have advanced. In this talk, a sampling of experimental findings from my research on water – oxide interactions will be presented with a focus on fundamental studies utilizing single crystal surfaces as models.

Dust particles play a major role in the physics and chemistry of the interstellar medium. After a discussion of the physical properties and molecular constituents of dust particles and how they are determined, I will mention current ideas concerning the chemistry that occurs both on the surfaces of bare dust particles and on the ices that first build up in cold cores. The different mathematical approaches to simulate surface chemical processes will be considered, and progress in using them reported.

NASA’s Laboratory Astrophysics Program supports a wide range of science investigations that enable or contribute significantly to the Agency’s strategic goals in astrophysics. Specifically, the Lab Astro data play an important role in both the development of the Agency’s space astrophysics missions, and in the realization of their full scientific potential. With an annual budget of ca. $3M, Laboratory Astrophysics represents only one element of the multifaceted Astrophysics Research and Analysis (APRA) Program, which, itself, is just one component of the Astrophysics Division’s Strategic Research and Technology (SR&T) portfolio. Therefore, in order to understand the constraints that bound the program and the opportunities that shape it, it is important to understand the program in this larger context. Toward this end, in this talk we will review the status of the NASA’s Lab Astro Program, as well as that of the larger programmatic and organizational landscape within which the program resides.

Understanding whether or not the interstellar dust at high redshifts is similar to dust at low redshifts is central to correctly interpreting observations of the distant Universe and for understanding the evolution of interstellar dust. Strong absorption lines in quasar spectra, arising in galaxies along the sight-lines, allow us to study interstellar matter for > 90% of the age of the Universe. We measure the dust content of absorber galaxies with element depletions derived from relative abundances such as [Fe/Zn] or [Cr/Zn]. Combining > 800 quasar spectra, we found a small but significant amount of dust in quasar absorbers at redshifts 1 < z < 2, and that on average, the dust extinction in most quasar absorbers is similar to that in the Small Magellanic Cloud, with no 2175 A bump. However, a small number of the systems appear to be far more dusty, with detectable 2175 A bumps and large reddening of the background quasars. We have been carrying out the first study of interstellar silicates in such dusty quasar absorbers with mid-infrared Spitzer spectroscopy. Our results so far indicate the detection of the 10 micron silicate absorption feature, which appears to be best-fitted with laboratory measurements of amorphous olivine. The strength of the silicate absorption seems to correlate with reddening, but more steeply than seen in the diffuse interstellar clouds of the Milky Way. We will discuss how the strength of the silicate feature in these distant galaxies correlates with the gas metallicity and how silicate and carbonaceous dust contents compare. These studies are providing fresh insights into the growth and survival of cosmic dust in chemically young environments over the past 10 billion years.

A variety of complex organic molecules have been detected in the interstellar medium, but the chemical pathways to these molecules are not well-understood. Grain surface chemistry plays a fundamental role in their formation, and radical-radical combination reactions on ice surfaces form these molecules during star formation. These radicals form from photolysis of interstellar ice constituents, including water, methanol, ammonia, and formaldehyde. Methanol photodissociation is a major source source of radicals that ultimately react to form complex organics. However, the branching ratios for this process are not well-characterized. To this end, we are conducting laboratory measurements of methanol photodissociation via quantitative therahertz (THz) spectroscopy. We are also using chemical modeling to test the effects of these branching ratios on the formation of complex organics in interstellar environments. Here we present the initial results of the laboratory and modeling work and discuss the implications of these results for interstellar complex organic chemistry.

The discovery of high-redshift GRBs opens a new window into the nature of dust in the early universe. We explore the dust properties of the host galaxies of ~40 long-duration GRBs at 2.0≤ z ≤ 6.7, with a mean redshift of z=3.34 (corresponding to a look-back time of 1.94 Gyr), by fitting their ultraviolet optical-near-IR afterglow spectral energy distributions. We find that the average dust extinction in the visual band is A_V~0.3 mag. The E(B-V)/N_HI and A_V/N_HI ratios decrease linearly with the dust-to-gas ratio, suggesting that the dust properties remain unchanged at the epoch of 2.0≤ z ≤ 6.7. The inferred extinction curves are closely reproduced in terms of a mixture of amorphous silicate and graphite. The dust properties do not appear to evolve with z in the interval 2.0≤ z ≤ 6.7.

During the cold stages of star- and planet-formation, icy grain mantles constitute a major reservoir of molecules, especially H2O, CO2 and CO. Heating of these ices by the newly formed star increases the mobility of molecules and radicals in the ice, resulting in ice segregation and radical-radical chemistry, as well as sequential evaporation into the gas phase. Thermal ice processes are thus crucial for the chemical evolution both on grains and in the gas phase. In this talk I will discuss laboratory attempts on quantifying the effects of ice heating and especially segregation of and evaporation from H2O-rich ice mixtures. These studies have been directly motivated by astrophysical observations of ice and gas around protostars, and the contents of comets in our own solar system. I will end with discussing the interoperation of such observations from e.g. Spitzer in light of the most recent thermal ice experiments.

It is well known that electronic excitation of surfaces and interfaces leads to chemical modification and transformation. These “transformations” can be brought about by photon-, electron- or ion-impact and can occur in radiation environments within the interstellar media or near star forming regions. Since the chemical modification processes are inherently non-equilibrium, the chemical products are often rather exotic and not easily produced under normal thermal conditions. This is particularly true for complex targets such as mixed low-temperature ices. For mixed ices, one must also consider trapped molecules and buried interfaces. This talk will emphasize some of our group’s recent experimental activities in low-energy (5-50 eV) electron and ultraviolet photon (6.3 eV) induced reactions in mixed ices. We will specifically examine the formation of H2, O2, CO2 and CO during the irradiation of water ice containing methane and nanoscale ice films on graphitic surfaces.

The infrared (IR) spectra of most galactic and many extragalactic objects are dominated by emission features at 3.3, 6.2, 7.7, 8.6 and 11.2 micron, the so-called unidentified infrared (UIR) bands. These bands are now generally attributed to the IR fluorescence of Polycyclic Aromatic Hydrocarbon molecules (PAHs) and closely related species. It is now firmly established that the detailed characteristics of the PAH bands exhibit significant variability from source to source and spatially within extended sources. These variations reflect the physical conditions in the emission zones and composition of the emitting materials. Underpinning of these observations with laboratory measurements and theoretical calculations of spectra from PAHs and related species is a fundamental necessity in order to allow exploitation of these features as astrophysical probes. Here, I will review the spectral characteristics of PAHs in space and the recent advances made by comparison of the astronomical PAH spectra with laboratory experiments and theoretical calculations of PAH spectra.

As the second most abundant interstellar molecule, carbon monoxide, CO, plays very important role in astrochemistry. It's also used as a tracer to determine various physical parameters of astronomical objects. Very recently, CO collisional rates with H2 have been reevaluated, especially for those at high rotational energy levels (Yang et al. 2010). To investigate the effects of the new rates, several cloudy PDR models have been applied with the two sets of the data: the "old" leiden data and the new estimation. As the result, CO emission lines' intensities of the rotational spectroscopy have been calculated. The rate changes introduce notable effects under certain physical conditions and are very important to astronomical studies. This work is supported by NSF (0607028 and 0908877) and NASA (07-ATFP07-0124).

The low abundances of O2 and H2O in the gas phase of molecular clouds have been a continuing problem to modelers of the chemistry of these regions. Steady state models give much too high values comparing to upper limits of these two molecules based on SWAS and Odin observations. This work continues the study of Quan et al. 2008. Apart from the gas phase chemistry discussed in detail in Quan et al. 2008, dust grains play important roles in interstellar chemistry and affect gas phase abundances. Here we present our recent study of application of a serial of gas-grain models in which physical conditions were varied.In the poster, the role of the dust grains to explain the possible low abundances of gaseous O2 and H2O will be illustrated and the possible places where these two molecules may have big abundances will be suggested.

We have observed the Orion star forming region from 223-251 GHz using the wideband lambda = 1.3 mm receiver at the Caltech Submillimeter Observatory (CSO). After double sideband spectral deconvolution, a noise level of approximately 30 mK was obtained. The low noise level in these observations allows identification of many more lines than were observed in previous broadband surveys. A total of 5378 spectral lines with an intensity >3-sigma have been identified in this survey. Line assignment and spectral analysis initially focused on those molecules previously identified in spectral surveys toward this source. Many newly identified weak transitions of previously detected molecules came from this initial analysis. Spectral lines from isotopologues and excited vibrational states of previously detected molecules have also been identified. Full assignment of this observational spectrum is limited by the lack of sufficient laboratory spectral information available in catalogs like the JPL and CDMS spectral line databases. Comparison with these databases only allows assignment of ~20% of the identified spectral features. In addition, the large amount of spectral data obtained in this broadband survey makes traditional by-eye assignment techniques inefficient. We will report on the progress of the spectral line assignment of the Orion survey, the tools that we are developing to aid in analysis, and the need for additional spectroscopic studies to aid in line identification.

Multi-component solids can have surfaces that differ from any bulk-like termination. The surface can even be nonstoichiometric, depending on the ambient conditions. In this lecture, we will discuss the methodology for determining the preferred surface composition and termination, and how this depends on the bulk material structure and the ambient conditions. The implications for surface chemistry and astrophysical applications of these effects will be discussed.

In order to determine the column density of an ice component, the band strength of an absorption feature must be known. The sizes of near-IR features can be correlated with a previously studied mid-IR feature whose band strength is already known. Molecules in mixtures may affect position, FWHM, shapes and intensities of absorption peaks, as well as band strength. Many satellites within the solar system have surfaces are dominated by either N2 or H2O (Review by Roush 2001). It has already been shown that for CH4 and CO isolated in N2 the peak positions will be shifted, and width and peak intensities will be altered in comparison to pure ice spectra (Quirico et al. 1999). The experiments here focus on changes in band strength, intensity, FWHM, and positioning for N2 mixed with CO, CO2, CH4, and NH3 in 5:1 ratios and H2O mixed with CO, CO2, CH4, and NH3 in 5:1 ratios and is a continuation of previous results published by the Astro- and Solar-System Program at UAB (Gerakines et. al. 2005). These data may be used to determine ice abundances from observed near-IR spectra or to predict the sizes of near-IR features in astrophysical environments.

Absolute doubly differential electron emission yields from thin films of amorphous ice following the transmission of 6-MeV protons and 1-MeV/u fluorine ions are presented. The ice films were condensed on a cryogenic 1-μm copper foil substrate held at 40 K. The absolute doubly differential yields are compared to results from Monte Carlo track structure simulations for electron transport in liquid water. The model shows good agreement with the experimental data for electron energies greater than approximately 50 eV, but tends to overestimate the yields of low-energy electrons.

In this talk, I will give an overview of a newly funded facility centered on the production and extraction of highly charged ions (HCIs) at Clemson University. Specifically, I will discuss first the electron beam ion trap (EBIT) source, which is used to produce HCIs in a controlled laboratory setting. Additionally, I will outline our designs for an HCI beamline and its associated target and sample preparatory stations. My purpose is to introduce our facility as a project "in-progress" and to solicit useful ideas from participants as to how this can best be configured and utilized as a user facility for laboratory astrophysics. To facilitate that discussion, recent examples of the successful use of EBITs for ground-based astrophysics will be presented.

Silicate dust plays an essential role in many astrophysical environments. The “amorphous” silicate spectral features have been observed in our solar system, young stellar objects, star formation regions, novae, and the diffuse and dense interstellar medium as well as in extragalactic environments such as quasars and AGN. This dust contributes to the physical processes inherent in star formation processes, as well as to several aspects of interstellar processes such as gas heating and the formation of molecules. The discovery of this almost ubiquitous ~10um “amorphous” silicate feature, combined with the more recent discovery of crystalline silicate spectral features in many environments, led to many laboratory studies of potential cosmic dust analogs attempting to determine the exact nature of this dust. New laboratory data combined with re-analysis of observational data for asymptotic giant branch (AGB) stars will be presented. Combined, these data present a challenge to the "common wisdom" on what we think we know about silicates in space. Furthermore, we suggest that new laboratory data is needed to break the degeneracy of similar spectral features arising from different dust species. In particular the competing effects of compositions, grain shape and temperature on spectral parameters needs to be fully investigated.

Formation of H2 in interstellar gas occurs primarily via surface reactions on grains. A key parameter in determining the efficiency of H2 formation is the probability for H to stick to the surface. Once H2 is formed it may return to the surface and participate in further reactive processes. However, little is known about the sticking probability of H2 on grains. Simulations of the sticking coefficient for molecular hydrogen on the icy mantles of interstellar dust using a model based on classical molecular dynamics (MD) are being developed. The current study is on a simulated surface of amorphous ice with molecular hydrogen incident on the surface with different velocities. After a series of MD runs with different set of initial conditions based on the observed and known interstellar dust and gas temperatures, the sticking coefficient is then calculated as a function of the gas and dust temperatures. We present some preliminary work here. This pro ject is supported by NASA grant NNG06GJ11G from the Astro- physics Theory Program

After a brief summary of major findings from laboratory work on the formation of molecular hydrogen on surfaces in simulated space conditions, we present recent studies on the influence of surface morphology on the formation of molecular hydrogen on silicates and on analogues of aerosol particles in planetary atmospheres. Through calculations and computer simulations of experimental data we characterize the influence of surface properties on the processes leading to molecular hydrogen formation. The determination of the energetics of molecule formation on and ejection from interstellar and planetary dust grain analogs is important for building reliable models of the chemical evolution of interstellar clouds and of planetary atmospheres. These new calculations take into account the heterogeneous morphology of the surface, and thus obtain a more faithful picture of the processes occurring on realistic analogs of interstellar or aerosol particles. Furthermore, using computer simulations and data obtained in the laboratory, we calculated the efficiency of molecule formation in actual space environments. This research was done in collaboration with Prof. Ofer Biham's group (the Hebrew University). It was partially supported with grants from NASA (Astronomy and Physics Research and Analysis), NSF (Astronomical Sciences) and BSF (Binational Science Foundation).

Gas phase ion-molecule reactions have long been thought to be the main formation mechanism for complex organic molecules in star-forming regions. However, calculations have shown that gas-phase reactions are inefficient for the formation of methyl formate [Horn et al., ApJ 611, 2004], which is one of the most abundant complex organics in the interstellar medium (ISM). It is clear that the chemical models for interstellar organic chemistry need to be revised, and that grain surface reactions play a more important role in the complex organic chemistry of the ISM than was previously assumed. A recent astrochemical modeling study [Garrod, Widicus Weaver, and Herbst, ApJ 682, 2008] indicates that radical-radical combination reactions on interstellar grain surfaces are indeed efficient processes for forming complex organic molecules. In this talk, I will present an overview of the dominant grain surface processes thought to give rise to complex organic chemistry in interstellar ices. I will also suggest additional laboratory and computational studies that are needed to achieve a better understanding of these processes, and give an update on our group's progress toward some of these measurements. Lastly, I will report on our most recent work in astrochemical modeling that focuses on the influence of methanol photolysis branching ratios on complex organic chemistry in the ISM.