title: Dissociation of internal energy-selected methyl bromide ion revealed from threshold photoelectron-photoion coincidence velocity imaging.
abstract: Dissociative photoionization of methyl bromide (CH3Br) in an excitation energy range of 10.45-16.90 eV has been investigated by using threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging. The coincident time-of-flight mass spectra indicate that the ground state X(2)E of CH3Br(+) is stable, and both A(2)A1 and B(2)E ionic excited states are fully dissociative to produce the unique fragment ion of CH3 (+). From TPEPICO 3D time-sliced velocity images of CH3 (+) dissociated from specific state-selected CH3Br(+) ion, kinetic energy release distribution (KERD) and angular distribution of CH3 (+) fragment ion are directly obtained. Both spin-orbit states of Br((2)P) atom can be clearly observed in fast dissociation of CH3Br(+)(A(2)A1) ion along C-Br rupture, while a KERD of Maxwell-Boltzmann profile is obtained in dissociation of CH3Br(+)(B(2)E) ion. With the aid of the re-calculated potential energy curves of CH3Br(+) including spin-orbit coupling, dissociation mechanisms of CH3Br(+) ion in A(2)A1 and B(2)E states along C-Br rupture are revealed. For CH3Br(+)(A(2)A1) ion, the CH3 (+) + Br((2)P1/2) channel is occurred via an adiabatic dissociation by vibration, while the Br((2)P3/2) formation is through vibronic coupling to the high vibrational level of X(2)E state followed by rapid dissociation. C-Br bond breaking of CH3Br(+)(B(2)E) ion can occur via slow internal conversion to the excited vibrational level of the lower electronic states and then dissociation.
authors: Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China.
authors: Xiaofeng
authors: X
authors: Tang
authors: Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China.
authors: Xiaoguo
authors: X
authors: Zhou
authors: Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China.
authors: Zhongfa
authors: Z
authors: Sun
authors: Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China.
authors: Shilin
authors: S
authors: Liu
authors: National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, China.
authors: Fuyi
authors: F
authors: Liu
authors: National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, China.
authors: Liusi
authors: L
authors: Sheng
authors: Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China.
authors: Bing
authors: B
authors: Yan