VUV spectroscopy and photo-processing of astrochemical ices: an experimental study

Abstract

In order to understand much of the chemistry that underpins astronomical phenomena (e.g. star and planet formation) it is essential to probe the physico-chemistry of ice surfaces under astronomical conditions. The physical properties and chemical reactivity of such icy surfaces depends upon its morphology. Thus it is necessary to explore how the morphology of astrochemical ices is influenced by their local environment (e.g. temperature and pressure) and the mechanisms by which they are processed. In this paper we report the results of a series of experiments to explore the morphology of a variety of molecular ices using VUV spectroscopy. Spectral signatures are found that may allow the morphology of such ices to be identified.

Vacuum-UV spectroscopy of interstellar ice analogs

“…Error margins corresponding to the values in the second and third column are ±0.4 nm and ±0.03 eV. The peak positions agree with previous works, see Mason et al (2006), Lu et al (2005), and Brith & Schnepp (1965). Table 4.…”

“…Figure 3 displays the CO fourth positive band system; it is attributed to the A 1 Π ← X 1 Σ + system. Table 3 summarizes the transition, band position, and area of each feature at 8 K. We were able to observe twelve bands identified as (0, 0) to (11,0) where the (0, 0), (1, 0), and (2, 0) bands present a Davydov splitting, in agreement with Mason et al (2006), Lu et al (2005), and Brith & Schnepp (1965). Like Mason et al (2006), we were unable to observe the (12, 0) transition reported by Brith & Schnepp (1965) and Lu et al (2005), because of the low intensity Fig.…”

“…O 2 , N 2 , and CH 4 were reported by Mason et al (2006), Kuo et al (2007), and Lu et al (2008). But the VUV-absorption cross sections were only estimated for solid H 2 O, NH 3 , and CO 2 (Mason et al 2006).…”

“…But the VUV-absorption cross sections were only estimated for solid H 2 O, NH 3 , and CO 2 (Mason et al 2006). Furthermore, all previous works have been performed using synchrotron monochromatic light as the VUV-source, scanning the measured spectral range.…”

Electron, proton and ion induced molecular synthesis and VUV spectroscopy of interstellar molecules in the ice phase

“…In our experiments molecular oxygen was deposited at a pressure of 1 × 10 −7 mbar onto a cold CaF 2 window, kept at ∼25 K, for different exposure times (15, 20, 25 and 32 second) and VUV spectra were recorded. The feature peaking at 180 nm was assigned to the (O 2 ) 2 , dimer (Mason et al 2006). The band was very weak when using thin O 2 ice layers but grew in intensity with increased deposition to form a thick O 2 ice (Figure 1).…”