Systematic investigation of CO : NH ice mixtures using mid-IR and VUV spectroscopy - part 2: electron irradiation and thermal processing.

Many experimental parameters determine the chemical and physical properties of interstellar ice analogues, each of which may influence the molecular synthesis that occurs in such ices. In part 1, James , , 2020, , 37517, we demonstrated the effects that the stoichiometric mixing ratio had on the chemical and physical properties of CO : NH mixtures and the impact on molecular synthesis induced by thermal processing. Here, in part 2, we extend this to include 1 keV electron irradiation at 20 K of several stoichiometric mixing ratios of CO : NH ices followed by thermal processing.

The rise of an exciton in solid ammonia.

We trace a polymorphic phase change in solid ammonia films through the emergence of a Frenkel exciton at 194.4 nm, for deposition temperatures of 48 K, 50 K and 52 K. Observations on a timescale of hours give unparalleled access to the individual processes of nucleation and the phase change itself.

Systematic investigation of CO : NH ice mixtures using mid-IR and VUV spectroscopy - part 1: thermal processing.

The adjustment of experimental parameters in interstellar ice analogues can have profound effects on molecular synthesis within an ice system. We demonstrated this by systematically investigating the stoichiometric mixing ratios of CO : NH ices as a function of thermal processing using mid-IR and VUV spectroscopy. We observed that the type of CO bonding environment was dependent on the different stoichiometric mixing ratios and that this pre-determined the NH crystallite structure after phase change.

Crystallites and Electric Fields in Solid Ammonia.

Absorption spectra of vacuum-deposited films of ammonia have been obtained in the range 115 nm to 310 nm for a set of 15 deposition temperatures, T, between 20 K and 80 K. Results focus upon the region 115 nm to 130 nm in overlapping D, E, F and G←X Rydberg transitions involving Wannier-Mott excitons. We identify two phases of ammonia, showing the solid to be polymorphic.

VUV spectroscopy of an electron irradiated benzene : carbon dioxide interstellar ice analogue.

We present the first vacuum ultraviolet spectroscopic study of an interstellar ice analogue of a 1 : 100 benzene (CH) : carbon dioxide (CO) mixture which has been energetically processed with 1 keV electrons. We have exploited the fact that benzene has a relatively high photoabsorption cross section in the vacuum ultraviolet region to study this dilute mixture of benzene. Before irradiation with 1 keV electrons, we observed that the benzene electronic transition bands in the CH : CO mixture exhibits a blueshift in band position towards energies observed in the gas-phase compared with that of pure, amorphous benzene and we have attributed this to a matrix isolation effect.

The optical absorption spectra of spontaneously electrical solids: the case of nitrous oxide.

Absorption spectra of films of N2O, in the range 115-160 nm, are presented for deposition temperatures between 33 K and 64 K. Observed shifts in the absorption energy vs. deposition temperature are analysed in terms of the temperature-dependent spontaneously electrical ('spontelectric') fields present in the films.