Using Ion-velocity Map Imaging Technique to Study Photodissociation of 2-Bromopentane

The photodissociation dynamics of 2-bromopentane at ～234 nm has been investigated by utilizing ion-velocity map imaging technique. The mapped images of Br(²P_3/2) (denoted as Br) and Br(²P_1/2) (denoted as Br*) fragments were analyzed by means of the speed and angular distributions, respectively. The speed distributions can be fitted with two Gaussian components which are correlated to the two independent reaction paths on the excited po-tential energy surfaces (PES). The high-energy component is from the prompt dissociation along the C-Br stretching mode, while the low-energy one is related to the dissociation from the coupling of the C-Br stretching and bending modes. Relative quantum yield is measured to be 0.892 for Br in the photodissociation of 2-bromopentane at 234 nm. Com-bining the anisotropy parameter with the relative quantum yield of Br and Br* fragments, the contributions of the excited ³Q₀，³Q₁, and ¹Q₁ states to the products Br and Br* were derived. The effect of alkyl branching on the mechanism of photodissociation was discussed by comparing the photodissociation processes of four isomers of bromopentane.