Production of O(¹D) following electron impact on CO₂

Abstract

We have studied the excitation of metastable O(1D) following dissociative excitation of CO2 in the electron impact energy range from threshold to 400 eV. A solid Ne matrix at ∼20 K forms the heart of the detector. This is sensitive to the metastable species through the formation of excited excimers (NeO*), The resultant excimer radiation is readily detected, providing a means of measuring the production of the metastables. Using a pulsed electron beam and time-of-flight techniques, we have measured the O(1D) kinetic energy spectrum and its relative production cross sections as a function of electron impact energy. Threshold energy data are used to gain information about the excitation channels involved. In addition, an emission excitation function for the red photons, emitted in coincidence with the exciting electron pulse, has been measured in the 0–400 eV energy range.

Detection of Metastable Atoms and Molecules using Rare Gas Matrices

“…This had first been noticed in early work where fluorescence following VUV irradiation of solid Ne containing traces of O 2 , N 2 O, or CO 2 was studied Maillard et al, 1982Maillard et al, , 1983Walker et al, 1981). This suggested that a Ne matrix could be used to detect 1 D atoms and this was in fact shown to be the case by Kedzierski et al (2010bKedzierski et al ( , 2013 using N 2 O and CO 2 targets. 1) in addition to the auroral green ( 1 S-1 D) feature.…”

Role of Suprathermal Chemistry on the Evolution of Carbon Oxides and Organics within Interstellar and Cometary Ices

“…Shirai et al compiled tables of cross sections for different processing that occur during the electron impact of CO 2 gas as a function of energy. However, since O­( 1 D) has a long lifetime, cross sections for its production were only recently estimated . Therefore, during radiation we can anticipate the major species produced: The formation of O → ( 3 P) is spin-forbidden, so the most likely products formed (at least initially) would be the O → ( 1 D) or O → ( 1 S) oxygen atoms, which, as we have seen, can insert into bonds or add across bonds, often without barrier.…”

“…However, since O( 1 D) has a long lifetime, cross sections for its production were only recently estimated. 51 Therefore, during radiation we can anticipate the major species produced:…”

Oxygen atom reactions with C2H6, C2H4, and C2H2 in ices

“…Atoms are mobile down to lower temperatures than radical fragments and could therefore still diffuse and react in very cold environments. The O( 1 D) atom is the first electronically excited state of the oxygen atom, and can be generated by energetic processing (photolysis or electron impact) of common interstellar ice constituents including H 2 O, CO 2 , O 2 , and O 3 (Stief et al 1975;Slanger & Black 1971;Cosby 1993;Lee et al 1977;DeMore 1966;Kedzierski 2013). Of particular importance, Lyman-α photolysis of H 2 O and CO 2 produces an O( 1 D) atom with 10% and 100% efficiency respectively.…”