Photodissociation of 2-Bromobutane at ∼265 nm by Ion-velocity Map Imaging Technique

Abstract

The photodissociation dynamics of 2-bromobutane has been investigated at 264.77 and 264.86 nm by ion-velocity map imaging technique coupled with resonance-enhanced multi-photon ionization. The speed and angular distributions have been derived from the velocity map images of Br and Br*. The speed distributions of Br and Br* atoms in the photodissociation of 2-bromobutane at ∼265 nm can be fitted using only one Gaussian function indicating that bromine fragments were produced via direct dissociation of C—Br bond. The contributions of the excited 3Q0, 3Q1, and 1Q1 states to the products (Br and Br*) were discussed. It is found that the nonadiabatic 1Q1 ← 3Q0 transition plays an important role for Br photofragment in the dissociation of 2-C4H9Br at ∼265 nm. Relative quantum yield of 0.621 for Br(2P3/2) at ∼265 nm in the photodissociation of 2-bromobutane is derived. By comparing the photodissociation of 2-C4H9Br at ∼265 nm and that that at ∼234 nm, the anisotropy parameter β(Br) and β(Br*), and relative quantum yield Φ(Br) decrease with increasing wavelength, the probability of curve crossing between 3Q0 and 1Q1 decreases with increasing laser wavelength.