The solid phase photolysis and radiolysis of ethylene at 20 to 77 K

Abstract

Fi lms of e th y le n e co nd e nse d o nt o a co ld fin ge r ma int a ine d a t 20 K we re ir radi a ted with ph ot o ns wh ose e ne rgy ra nged fro m 8.4 to 21.2 e V. At th e h ig he r ph oto n e ne rgies th e re la tiv e yie ld s of produ c ts co mp a re we ll with th ose see n in th e radi o lys is o f so lid e th y le ne. Expe rime nt s o n C H2C D2 d e m o ns tra te th a t in th e p hoto lys is h ydrogen is ma inl y fo rm ed b y th e e limin a ti o n processes C H 2C D~ ---> H AD 2)The re la tiv e proba biliti es o f th ese three pro-cesses a re ind e pe nd e nt o f th e e n e rgy o f th e in c id e nt p hoto ns fr o m 8.4 to 11. 6 e V a nd a re within expe rim e nt a l e rror id e ntic a l to th ose o bse rved in ea rl ie r g as p hase photolys is expe rim e nts . Re la t ive to ace tyle ne, cyc lo but a ne is a mi no r pro du c t a t 8.4 eV but in c reases b y a n o rd e r o f magn it ud e a t hi ghe r e ne rg ies wh e re ion s pla y a role. C yc lo buta n e , I · bute ne a nd me th ylcyclopro pa n e fo rm ed up on irradia tio n of froze n C 2H, -C 2D, mixtures cons isted ma inl y of C,DB, C.,D,H" a nd C.,H 8. Pl a us ib le m ec ha ni sm s wh ic h m ay acco u nt fo r th e fo r ma tio n of the la tt e r p rodu c ts a re exa min e d. In t he so lid p hase as in th e gas ph ase th e re la ti ve impo rta nce of H·a to m produ c t io n is see n to in c rease with in c reas in g ph oto n e ne rgy. Cyc lo propa ne, a ppa re ntl y form ed b y in se rtion of C H, int o C, H." is o bse r ved as a p rodu c t a t a ll wave · le n gth s in th e ph oto lys is, a nd in t he ra d io lys is. Key wo rd s: Et hy le ne; free rad ica l reac t ions; io n-m o lec u le reac ti o ns; ph oto lys is: po lyme ri zati o n ; ra d io lys is .

Implications for Extraterrestrial Hydrocarbon Chemistry: Analysis of Ethylene (C2H4) and D4-Ethylene (C2D4) Ices Exposed to Ionizing Radiation via Combined Infrared Spectroscopy and Reflectron Time-of-flight Mass Spectrometry

“…It is unlikely that these molecules are fragments of these molecules that are subliming at higher temperatures, as they are not reported as possible fragments at 10.49 eV (Lias et al 2016); however, even if these are fragments, the first peak does not overlap perfectly with the possible parent molecules, which shows that at least a certain amount if not all of the first peak is not from fragment ions and is from molecules ionized after sublimation. Until the present study C 3 H 6 was the only odd unit alkene detected as a product of ethylene ice irradiation (Tschuikow-Roux et al 1967;Gorden & Ausloos 1971;Kaiser & Roessler 1998); however, the current results show that many larger odd carbon unit alkene type molecules are formed from the processing of pure ethylene ices.…”

“…Finally, it is important to point out that none of these later sublimation events or any signal detected in this group (C n H 2n+2 ) can be due to fragmentation of larger molecules. These results are much more diverse than previous experiments, as Wagner (1962) was only able to detect products with even carbon units, and multiple other experiments (Gorden & Ausloos 1971;Strazzulla et al 2002;Compagnini et al 2009;Ennis et al 2011;Zhou et al 2014) did not detect any alkanes with an odd carbon unit. However, Kaiser & Roessler (1998) were able to assign alkane products containing both even and odd carbon units from C3 to C14.…”

“…The products identified from the ultraviolet photolysis of pure ethylene ice were acetylene (C 2 H 2 ), ethane (C 2 H 6 ), allene (C 3 H 4 ), cyclopropene (c-C 3 H 4 ), propene (C 3 H 6 ), cyclopropane (c-C 3 H 6 ), propane (C 3 H 8 ), methylcyclopropene (c-C 4 H 6 ), 1-butene (C 4 H 8 ), isobutene (C 4 H 8 ), trans-2butene (C 4 H 8 ), cis-2-butene (C 4 H 8 ), methyl cyclopropane (c-C 4 H 8 ), n-butane (C 4 H 10 ), and isobutane (C 4 H 10 ); the primary product was determined to be 1-butene (Tschuikow-Roux et al 1967). Gorden & Ausloos (1971) added to the literature the ultraviolet photolysis (8.4 eV, 10.0 eV, 11.6-11.8 eV, 21.2 eV) and γ-radiolysis of pure ethylene ice at 20 and 77 K, respectively, in order to determine the mechanism that ethylene undergoes to form larger hydrocarbons. The products analyzed with gas chromatographymass spectrometry (GC-MS) were determined to be molecular hydrogen (H 2 ), acetylene (C 2 H 2 ), propene (C 3 H 6 ), cyclopropane (c-C 3 H 6 ), 1-butene (C 4 H 8 ), 2-butene (C 4 H 8 ), cyclobutene (c-C 4 H 6 ), n-butane (C 4 H 10 ), cyclobutane (c-C 4 H 8 ), and at least eight hexene (C 6 H 12 ) isomers; no attempt was made to analyze molecules larger than C 6 products.…”

Photoionization of propylene, cyclopropane, and ethylene. The effect of internal energy on the bimolecular reactions of C2H+4 and C3H+6

“…At high er densities, where collisional stabilization of C4 Ht* is effective, the chemical studies in closed sys tems have provided a great deal of information concerning the various isomerization processes and structures associated with the intermediate ion [34,[38][39]. The present results concern the interactions of ethylene ions produced in the ground electronic state (the maxim urn photon e nergy of 11.…”

“…Th e overall reaction of CzHt with CZH4 has bee n subjected to considerable investigation in both th e closed sys te m photolysis [34 , [38][39] and radiolysis [34 ,39] as well as very extensively by kine ti c mass spectrom etry [4-5, 8, 18-29]. Th e evidence favors formation of an excited butene-lik e reaction intermediate whic h , at low pressures , deco mposes mainly into C3Ht and C4Ht…”