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Glycolaldehyde (HOCH2CHO) is a sugar-related interstellar prebiotic molecule that has been detected in two star-forming regions, Sgr B2(N) and G31.41+0.31. Glycolaldehyde is suspected to form from photodissociation-driven ice chemistry, and therefore can be used to trace complex organic chemistry in interstellar environments. The relative abundance of glycolaldehyde to its structural isomers, methyl formate (HCOOCH3) and acetic acid (CH3COOH), can be used to constrain astrochemical models. Given its central role in the complex chemistry of the interstellar medium, glycolaldehyde has been suggested as a prime molecular target for upcoming high-frequency molecular line searches using new far-infrared observatories. In particular, glycolaldehyde is a target for the Herschel Space Observatory HEXOS Key Program, which is conducting spectral line surveys of the Sgr B2(N) and Orion KL star-forming regions across the entire HIFI band. Laboratory investigation of glycolaldehyde in the HIFI frequency range is required before its lines can be identified in these spectra. We have therefore acquired the laboratory spectrum of glycolaldehyde in selected frequency ranges across the submillimeter range. We present here the laboratory spectral analysis of the ground vibrational state of glycolaldehyde up to 1.2 THz.

Although molecular oxygen, O2, has long been thought to be present in interstellar environments, it has only been tentatively detected toward one molecular cloud. The fractional abundance of O2 determined from these observations is well below that predicted by astrochemical models. Given the difficulty of O2 observations from ground-based telescopes, identification of a molecule that could be used as a tracer of O2 in interstellar environments would be quite useful. To this end, we have undertaken a collaborative examination of HO+ 2 in an attempt to evaluate the feasibility of its detection in interstellar clouds. We have conducted high-level ab initio calculations of its structure to obtain its molecular parameters. The reaction responsible for the formation of HO+ 2 is nearly thermoneutral, and so a careful analysis of its thermochemistry was also required. Using the Active Thermochemical Tables approach, we have determined the most accurate values available to date for the proton affinities of O2 and H2, and the enthalpy, Gibbs energy, and equilibrium constant for the reaction H+ 3 + O2- HO+ 2 + H2. We find that while this reaction is endothermic by 50 +- 9 cm-1 at 0 K, its equilibrium is shifted toward HO+ 2 at the higher temperatures of hot cores. We have examined the potential formation and destruction pathways for HO+ 2 in interstellar environments. Combining this information, we estimate the HO+ 2 column density in dense clouds to be [?]109 cm-2, which corresponds to line brightness temperatures of [?] 0.2 mK. If our results prove correct, HO+ 2 is clearly not a detectable interstellar molecule.

Although molecular oxygen, O2, has long been thought to be present in interstellar environments, it has only been tentatively detected toward one molecular cloud. The fractional abundance of O2 determined from these observations is well below that predicted by astrochemical models. Given the difficulty of O2 observations from ground-based telescopes, identification of a molecule that could be used as a tracer of O2 in interstellar environments would be quite useful. To this end, we have undertaken a collaborative examination of HO2+ in an attempt to evaluate the feasibility of its detection in interstellar clouds. We have conducted high-level ab initio calculations of its structure to obtain its molecular parameters. The reaction responsible for the formation of HO2+ is nearly thermoneutral, and so a careful analysis of its thermochemistry was also required. Using the Active Thermochemical Tables approach, we have determined the most accurate values available to date for the proton affinities of O2 and H2, and the enthalpy, Gibbs energy, and equilibrium constant for the reaction H3+ + O2 - HO2+ + H2. We find that while this reaction is endothermic by 50 +- 9 cm[?]1 at 0 K, its equilibrium is shifted toward HO2+ at the higher temperatures of hot cores. We have examined the potential formation and destruction pathways for HO2+ in interstellar environments. Combining this information, we estimate the HO2+ column density in dense clouds to be [?]109 cm[?]2, which corresponds to line brightness temperatures of [?] 0.2 mK. If our results prove correct, HO2+ is clearly not a detectable interstellar molecule.

Gas-phase processes were long thought to be the key formation mechanisms for complex organic molecules in star-forming regions. However, recent experimental and theoretical evidence has cast doubt on the efficiency of such processes. Grain-surface chemistry is frequently invoked as a solution, but until now there have been no quantitative models taking into account both the high degree of chemical complexity and the evolving physical conditions of star-forming regions. Here, we introduce a new gas-grain chemical network, wherein a wide array of complex species may be formed by reactions involving radicals. The radicals we consider (H, OH, CO, HCO, CH3, CH3O, CH2OH, NH, and NH2) are produced primarily by cosmic ray-induced photodissociation of the granular ices formed during the colder, earlier stages of evolution. The gradual warm up of the hot core is crucial to the formation of complex molecules, allowing the more strongly bound radicals to become mobile on grain surfaces. This type of chemistry is capable of reproducing the high degree of complexity seen in Sgr B2(N), and can explain the observed abundances and temperatures of a variety of previously detected complex organic molecules, including structural isomers. Many other complex species are predicted by this model, and several of these species may be detectable in hot cores. Differences in the chemistry of high- and low-mass star formation are also addressed; greater chemical complexity is expected where evolution timescales are longer.

Both grain surface and gas phase chemistry have been invoked to explain the disparate relative abundances of methyl formate and its structural isomers acetic acid and glycolaldehyde in the Sgr B2(N) star-forming region. While a network of grain surface chemistry involving radical-radical reactions during the warm-up phase of a hot core is the most chemically viable option proposed to date, neither qualitative nor quantitative agreement between modeling and observation has yet been obtained. In this study, we seek to test additional grain surface and gas phase processes to further investigate methyl formate-related chemistry by implementing several modifications to the Ohio State University gas/grain chemical network. We added two new gas phase chemical pathways leading to methyl formate, one involving an exothermic, barrierless reaction of protonated methanol with neutral formic acid; and one involving the reaction of protonated formic acid with neutral methanol to form both the cis and trans forms of protonated methyl formate. In addition to these gas phase processes, we have also investigated whether the relative product branching ratios for methanol photodissociation on grains influence the relative abundances of methyl formate and its structural isomers. We find that while the new gas phase formation pathways do not alter the relative abundances of methyl formate and its structural isomers, changes in the photodissociation branching ratios and adjustment of the overall timescale for warm-up can be used to explain their relative ratios in Sgr B2(N).