Pressure effects and quantum yields in the photolysis of ethylene and propene at 185 nm

Abstract

Gaseous ethylene and propene were photolysed with varying amounts of added nitrogen, oxygen, and other gases. The product analysis and variation of yields with added gas are consistent with the major primary reactions (i)-(v) for which the primary quantum yields were estimated. Several other minor primary reactions were found. The C2H4 + hv(A = 185 nm) + C2Ha + H,; 4 = 0.68 -+ C,H2 + 2H ; 4 = 0.20 --t C2H3+ H; + = 0 * 1 6 C3Hs + hv ( A = 185 nm) + CH2:CHCH,* + H ; 4 = 0.41 + C2H3* + CH,; 4 = 0.36 reactions are inhibited by the addition of inert gases ranging from He to CO,; the inhibition is, within experimental error, the same for each additive. Higher pressures were needed to inhibit the ethylene photolysis than other olefins studied and the effect is attributed to the smaller collision diameter of the excited state in ethylene. The results for propene can be explained by a mechanism involving two excited intermediates, only one of which is read i I y quenched .WE have shown that the gas-phase photolysis of simple olefins such as the butenes and pentenes can be inhibited by the presence of additives such as nitrogen, argon, and carbon dioxide. Owing to the peculiar effect of pressure on the yield of the geometrical isomer when either but-2-ene or pent-2-ene is photolysed, the results could be interpreted in terms of collisional deactivation of the singlet Rydberg state. In propene and particularly in ethylene the Rydberg state is found at higher energies than in other olefins and it is possible to excite only the V ( x , x * ) state rather than the Rydberg state, so it seemed worthwhile to conclude our studies by examining the pressure effects in these compounds.

A novel method to decompose two potent greenhouse gases: Photoreduction of SF6 and SF5CF3 in the presence of propene

“…Since neither SF 6 nor SF 5 CF 3 was able to react with propene in the dark, the photoreduction of SF 5 X in the presence of propene must be initiated by the excitation of propene. When exposed to VUV irradiation, propene would be excited into its continous → * band, and followed by dissociation into fragments corresponding to the following equation [29] C 3 H 6 184.9 nm −→ • CH 3 + • C 2 H 3 (1)…”

Photochemistry of C3Hphydrocarbons in Titan’s stratosphere revisited

“…Considering the studies of Borrell et al (1971) at 184 nm, of Lee et al (2003) at 157 nm as well as the theoretical study of Qu et al (2010), we considered the product yields to be those given in Table A.1.…”

Évaluation des ruptures de liaison α(C—H) centrale et terminale dans la photolyse du propène gazeux à 184,9 nm

“…I1 en est de mCme pour les rendements quantiques des quatre derniers produits. Cependant il y a quelques diffkrences qu'il faut discuter : Ctant donnC que les quantitCs des radicaux mCthyles et vinyles formCes devraient Ctre les mCmes (rkaction [3]), les rendements des but-2-knes (rCaction [17]) devraient Ctre voisins de ceux des penta-1,3-diknes (riaction [18]) et les rendements de l'isobutkne (rCaction [12]) proches de ceux de l'isoprkne (rCaction [22]). (Les rendements quantiques du cis-but-2Bne avec l'addition de SF, nous semblent erratiques : l'augmentation observCe pour l'ajout de 5 1 Torr de SF, i 1,7 Torr de M n'est pas confirmCe ?I plus hautre pression (tableau I).)…”