Infrared and reflectron time-of-flight mass spectroscopic study on the synthesis of glycolaldehyde in methanol (CH₃OH) and methanol–carbon monoxide (CH₃OH–CO) ices exposed to ionization radiation

Abstract

We present conclusive evidence on the formation of glycolaldehyde (HOCH2CHO) synthesized within astrophysically relevant ices of methanol (CH3OH) and methanol-carbon monoxide (CH3OH-CO) upon exposure to ionizing radiation at 5.5 K. The radiation induced chemical processes of the ices were monitored on line and in situ via infrared spectroscopy which was complimented by temperature programmed desorption studies post irradiation, utilizing highly sensitive reflectron time-of-flight mass spectrometry coupled with single photon fragment free photoionization (ReTOF-PI) at 10.49 eV. Specifically, glycolaldehyde was observed via the v14 band and further enhanced with the associated frequency shifts of the carbonyl stretching mode observed in irradiated isotopologue ice mixtures. Furthermore, experiments conducted with mixed isotopic ices of methanol-carbon monoxide (13CH3OH-CO, CH3(18)OH-CO, CD3OD-13CO and CH3OH-C18O) provide solid evidence of at least three competing reaction pathways involved in the formation of glycolaldehyde via non-equilibrium chemistry, which were identified as follows: (i) radical-radical recombination of HCO and CH2OH formed via decomposition of methanol--the "two methanol pathway"; (ii) via the reaction of one methanol unit (CH2OH from the decomposition of CH3OH) with one carbon monoxide unit (HCO from the hydrogenation of CO)--the "one methanol, one carbon monoxide pathway"; and (iii) formation via hydrogenation of carbon monoxide resulting in radicals of HCO and CH2OH--the "two carbon monoxide pathway". In addition, temperature programmed desorption studies revealed an increase in the amount of glycolaldehyde formed, suggesting further thermal chemistry of trapped radicals within the ice matrix. Sublimation of glycolaldehyde during the warm up was also monitored via ReTOF-PI and validated via the mutual agreement of the associated isotopic frequency shifts within the infrared band positions and the identical sublimation profiles obtained from the ReTOF spectra and infrared spectroscopy of the corresponding isotopes. In addition, an isomer of glycolaldehyde (ethene-1,2-diol) was tentatively assigned. Confirmation of the identified pathways based on infrared spectroscopy was also obtained from the observed ion signals corresponding to isotopomers of glycolaldehyde. These coupled techniques provide clear, concise evidence of the formation of a complex and astrobiologically important organic, glycolaldehyde, relevant to the icy mantles observed in the interstellar medium.

A study of interstellar aldehydes and enols as tracers of a cosmic ray-driven nonequilibrium synthesis of complex organic molecules

“…The experiments used a contamination-free UHV chamber (10 −11 torr) (15). The substrate consisted of a 1-cm 2 silver mirror interfaced to a cold finger and cooled to 5.5 ± 0.1 K. The processing of the ices and the infrared changes were probed online and in situ via FTIR spectroscopy.…”

On the Formation of Amide Polymers via Carbonyl–amino Group Linkages in Energetically Processed Ices of Astrophysical Relevance

“…Keck Research Laboratory in Astrochemistry (Jones & Kaiser 2013;Jones et al 2014;Kaiser et al 2014b;Maity et al 2014b) exploiting a next generation surface scattering machine. A gaseous mixture of ammonia (NH 3 , 99.99% Matheson TriGas) and carbon monoxide (CO, 99.9% Matheson TriGas) with a ratio of 8 to 5 at 260 Torr was deposited onto a 5.5±0.1 K silver target using a glass capillary array.…”

COMPLEX HYDROCARBON CHEMISTRY IN INTERSTELLAR AND SOLAR SYSTEM ICES REVEALED: A COMBINED INFRARED SPECTROSCOPY AND REFLECTRON TIME-OF-FLIGHT MASS SPECTROMETRY ANALYSIS OF ETHANE (C2H6) AND D6-ETHANE (C2D6) ICES EXPOSED TO IONIZING RADIATION

“…The present study employs an alternative method of tunable photoionization coupled with reflectron time-of-flight mass spectrometry (PIReTOF-MS) to unravel the complex chemistry taking place in the irradiated ethane ices. The incorporation of fragment-free single photon soft photoionization utilizing tunable vacuum ultraviolet light (VUV) has previously demonstrated the feasibility of this approach (Jones & Kaiser 2013;Kaiser et al 2014Kaiser et al , 2015Maity et al 2014aMaity et al , 2014bMaity et al , 2015Förstel et al 2015;Maksyutenko et al 2015;Turner et al 2015Turner et al , 2016Abplanalp et al 2016). The products released into the gas phase are photoionized and sampled via a reflectron time-offlight mass spectrometer, which monitors the complete product spectrum simultaneously based on the mass-to-charge ratios of the neutral molecules after their ionization.…”

“…Furthermore, the concurrent monitoring of both the ice (FTIR) and gas phases (PI-ReTOF-MS) allows for a cross correlation of the data to extract more accurately which infrared peaks belong to which molecule based on their appearance in the PI-ReTOF-MS data and decline in the FTIR spectra. In summary, PI-ReTOF-MS coupled with FTIR has been established as a powerful tool fordetecting the complete inventory of molecules formed in laboratory astrophysics experiments (Jones & Kaiser 2013;Kaiser et al 2014Kaiser et al , 2015Maity et al 2014aMaity et al , 2014bMaity et al , 2015Förstel et al 2015;Maksyutenko et al 2015;Turner et al 2015Turner et al , 2016Abplanalp et al 2016). References.…”