As a result of the deliberations and discussions during the last General Assembly of the IAU in The Hague, it was recommended that Commission 14 become a commission of the Executive Committee. The special interdisciplinary role and nature of Comm. 14 were in this way recognized and encouraged.

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Commission 14: Atomic and Molecular Data

Laboratory studies of the radiation chemistry occurring in astrophysical ices have demonstrated the dependence of this chemistry on a number of experimental parameters. One experimental parameter which has received significantly less attention is that of the phase of the solid ice under investigation. In this present study, we have performed systematic 2 keV electron irradiations of the amorphous and crystalline phases of pure CH3OH and N2O astrophysical ice analogues. Radiation-induced decay of these ices and the concomitant formation of products were monitored in situ using FT-IR spectroscopy. A direct comparison between the irradiated amorphous and crystalline CH3OH ices revealed a more rapid decay of the former compared to the latter. Interestingly, a significantly lesser difference was observed when comparing the decay rates of the amorphous and crystalline N2O ices. These observations have been rationalised in terms of the strength and extent of the intermolecular forces present in each ice. The strong and extensive hydrogen-bonding network that exists in crystalline CH3OH (but not in the amorphous phase) is suggested to significantly stabilise this phase against radiation-induced decay. Conversely, although alignment of the dipole moment of N2O is anticipated to be more extensive in the crystalline structure, its weak attractive potential does not significantly stabilise the crystalline phase against radiation-induced decay, hence explaining the smaller difference in decay rates between the amorphous and crystalline phases of N2O compared to those of CH3OH. Our results are relevant to the astrochemistry of interstellar ices and icy Solar System objects, which may experience phase changes due to thermally-induced crystallisation or space radiation-induced amorphisation. 

/pdf/comparative-electron-irradiations-of-amorphous-and-3irt8k1e.pdf

Comparative electron irradiations of amorphous and crystalline astrophysical ice analogues

Laboratory studies of the radiation chemistry occurring in astrophysical ices have demonstrated the dependence of this chemistry on a number of experimental parameters. One experimental parameter which has received significantly less attention is that of the phase of the solid ice under investigation. In this present study, we have performed systematic 2 keV electron irradiations of the amorphous and crystalline phases of pure CH3OH and N2O astrophysical ice analogues. Radiation-induced decay of these ices and the concomitant formation of products were monitored in situ using FT-IR spectroscopy. A direct comparison between the irradiated amorphous and crystalline CH3OH ices revealed a more rapid decay of the former compared to the latter. Interestingly, a significantly lesser difference was observed when comparing the decay rates of the amorphous and crystalline N2O ices. These observations have been rationalised in terms of the strength and extent of the intermolecular forces present in each ice. The strong and extensive hydrogen-bonding network that exists in crystalline CH3OH (but not in the amorphous phase) is suggested to significantly stabilise this phase against radiation-induced decay. Conversely, although alignment of the dipole moment of N2O is anticipated to be more extensive in the crystalline structure, its weak attractive potential does not significantly stabilise the crystalline phase against radiation-induced decay, hence explaining the smaller difference in decay rates between the amorphous and crystalline phases of N2O compared to those of CH3OH. Our results are relevant to the astrochemistry of interstellar ices and icy Solar System objects, which may experience phase changes due to thermally-induced crystallisation or space radiation-induced amorphisation.

https://pubs.rsc.org/en/content/articlepdf/2022/cp/d2cp00886f

Comparative electron irradiations of amorphous and crystalline astrophysical ice analogues.

Imidogen (NH) is the simplest nitrogen hydride that plays an important role in combustion and interstellar chemistry, and its combination with H2O is the prototypical amidation reaction of O-H bonds involving a nitrene intermediate. Herein, we report the observation of the elusive water complex of NH, a prereaction complex associated with the amidation reaction in a solid N2 matrix at 10 K. The hydrogen-bonded structure of NH···OH2 (versus HN···HOH) is confirmed via IR spectroscopy with comprehensive isotope labeling (D, 18O, and 15N) and quantum chemical calculations at the UCCSD(T)/aug-cc-pVQZ level of theory. In line with the observed absorption at 350 nm, irradiation of the complex at 365 nm leads to O-H bond insertion, yielding hydroxylamine NH2OH.

Water Complex of Imidogen.

85Mapping the evolution of pure CO2 ices irradiated by ions, UV, and electrons using the upgraded PROCODA code (employing an effective rate constant ordering by thermochemistry data)

Mid-IR and VUV Spectroscopic Characterisation of Thermally Processed and Electron Irradiated CO2 Astrophysical Ice Analogues

Shock Processing of Amorphous Carbon Nanodust

Ion induced processes play an important role in the chemical modification of astrophysical ices, both on the surfaces of satellites in the outer solar system and in the depths of dark molecular clouds where few photons penetrate. To date many laboratory studies have been developed to study energetic singly charged ion interactions with astrophysical ice analogues (e.g. (Mennella, et al(2004)), (Strazzulla, Baratta & Palumbo (2001)), (Gerakines, Moore, & Hudson (2000)) and have been found to produce new chemical species and cause significant effects on ice morphology (Palumbo (2005)). However, the effects of low energy and multiply charged ions have not yet been investigated. Such ions are prevalent in many astrophysical environments: as primary and secondary particles generated by cosmic ray bombardment and as constituents of planetary magnetospheres (e.g. Jupiter and Saturn). These ions comprise a rich variety of reactive species in a variety of charge states with typical kinetic energies of few keV. The effect of slow, multiply charged ions (MCIs) with the surfaces of astrophysical ices and their possible effect on chemical processing is unclear. However, studies of MCI impacts with insulator surfaces suggest that they may play an important role due to surplus potential energy imparted at the surface of the target (Winter & Aumayr (2001)). We have developed a research program to study ion interactions with astrophysical ices using an Electron Cyclotron Resonance (ECR) ion source at Queens University Belfast. Such a source can produce different species of ions with variable energy and different charge states. Ices are prepared in situ by depositing gas onto a cold infrared transmitting window. Samples are analysed using FTIR spectroscopy during irradiation. We have conducted a series of experiments to investigate the effects of ion charge state (potential vs. kinetic energy effects), ion energy (nuclear vs. electronic stopping processes) and sample temperature. In this poster we present the results of irradiation of low and high temperature H2O ice films with C n+ (n = 1, 2, 4) ions at 2 4 keV. The significance of the results will be discussed and possible reaction pathways for the formation of new products (CO and CO2) proposed.

Low energy singly and multiply charged ion irradiation of astrophysical ices

The recent discovery of hydroxylamine (NH2OH) molecule in the interstellar medium emphasizes the need to study the molecule in laboratory astrochemical ice analogues. Here, we present the first vacuum ultraviolet photoabsorption spectrum of hydroxylamine ice synthesized in-situ in an ammonia–oxygen (6:1) ice mixture irradiated by ~ 10 eV photons from synchrotron radiation source. The appearance of a new band between the 180–240 nm, with a band centered at ~ 207 nm, is assigned to the characteristic absorption of hydroxylamine molecule in the ice phase. This band maybe used in ammonia dominated, oxygen bearing, icy surfaces for the identification of hydroxylamine. 

https://hal.science/hal-03629815/document

N. J. Mason

Papers

Mid-IR and VUV Spectroscopic Characterisation of Thermally Processed and Electron Irradiated CO2 Astrophysical Ice Analogues

Shock Processing of Amorphous Carbon Nanodust

Low energy singly and multiply charged ion irradiation of astrophysical ices

Vacuum ultraviolet photoabsorption spectra of an in-situ synthesized peptide precursor: hydroxylamine on a cold astrochemical dust analogue

Ultraviolet Spectrum Reveals the Presence of Ozone on Jupiter's Fourth Moon Callisto