IR and UV photolysis of 1,3-cyclohexadiene. Evidence for formation of vibrationally excited 1,3,5-hexatriene

Abstract

The KrF and SF₆-sensitized CO₂ laser-induced photodissociation of 1,3-cyclohexadiene produce the same major products - cis- and trans- 1,3,5-hexatriene (HT), benzene and H₂, with relative yields strongly dependent on the source of excitation and the substrate pressure. From the time evolution of the nascent products, the rate constant for dissociation of 1,3-cyclohexadiene is estimated to be > 4 × 10⁷ and 8 × 10⁵ s^-1, respectively, in UV and IR photolysis. The UV absorption spectrum of the transient HT with a red-shift of about 30 nm implies the formation of vibrationally hot HT. The vibrational temperature of the system is estimated from the relative yields of cis- and trans-HT. The benzene channel is suggested as originating from a relatively higher vibrational level than the HT channel.