Multiphoton dissociation dynamics of CH3Br

The state-resolved photodissociation dynamics of CH3Br+ cations are studied using a combination of slice imaging and velocity mapping. Parent ions are prepared by (2 + 1) two-photon resonant three-photon ionization of CH3Br through the 5s Rydberg state in the energy region 29 069.8-29 976.0 cm(-1). Analysis of the photoelectron spectra reveals that CH3Br + ions are produced in the spin-orbit ground electronic state with a wide distribution of vibrational excitation. The photodissociation of CH3Br+ produces CH3+(X) + Br(P-2(1/2))/ Br(P-2(3/2)) whose product state distribution shows substantial excitation in the umbrella mode of the CH3+ photofragment, especially when concurrently producing the Br(P-2(1/2)) channel. The shapes of the photofragment angular distributions clearly show the different dissociation mechanisms in the Br(P-2(1/2)) and Br(P-2(3/2)) channels. The dissociation dynamics of the 5s Rydberg state of CH3Br are also presented and analyzed.