title: Photodissociation study of ethyl bromide in the ultraviolet range by the ion-velocity imaging technique.
abstract: The photodissociation of ethyl bromide has been studied in the wavelength range of 231-267 nm by means of the ion velocity imaging technique coupled with a [2+1] resonance-enhanced multiphoton ionization (REMPI) scheme. The velocity distributions for the Br ((2)P(1/2)) (denoted Br*) and Br ((2)P(3/2)) (denoted Br) fragments are determined, and each can be well-fitted by a narrow single-peaked Gaussian curve, which suggests that the bromine fragments are generated as a result of direct dissociation via repulsive potential-energy surfaces (PES). The recoil anisotropy results show that beta(Br) and beta(Br*) decrease with the wavelength, and the angular distributions of Br* suggest a typical parallel transition. The product relative quantum yields at two different wavelengths are Phi(234nm)(Br*)=0.17 and Phi(267nm)(Br*)=0.31. The relative fractions of each potential surface for the bromine fragments' production at 234 and 267 nm reveal the existence of a curve crossing between the (3)Q(0) and (1)Q(1) potential surfaces, and the probability of curve crossing decreases with the laser wavelength. The symmetry reduction of C(2)H(5)Br from C(3v) to C(s) invokes a nonadiabatic coupling between the (3)Q(0) and (1)Q(1) states, and with higher energy photons, the probability that crossing will take place increases.
authors.affiliation: State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, PR China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Tang
authors.forename: Lei
authors.initials: L
authors.lastname: Ji
authors.forename: Rongshu
authors.initials: R
authors.lastname: Zhu
authors.forename: Zhengrong
authors.initials: Z
authors.lastname: Wei
authors.forename: Bing
authors.initials: B
authors.lastname: Zhang