We report on the photodissociation dynamics of CO2^＋ via its A2Пu,1/2 state using the scheme of [1＋1] photon excitation that is intermediated by the mode-selected A2Hu,1/2（Vl,V2,0） vibronic states. Photodissociation fragment exciation spectrum and images of photofragment CO＋ have been measured to obtain reaction dynamics parameters such as the available energy and the average translational energy. Combining with the potential energy functions of CO2^＋, the dissociation mechanism of CO2^＋ is discussed. The conformational variation of CO2^＋ from linear to bent on the photodissociation dynamics of CO2^＋ is verified.
We present a first velocity map imaging study on the 234 nm photodissociation dynamics of two carbon-chain branched alkyl bromides, neopentyl bromide （denoted as NPB） and tert- pentyl bromide （denoted as TPB）. Unlike the 234 nm photodissociation of the unbranched n-C5H11Br molecule where only a direct fission of the C-Br bond is involved, the branched NPB and TPB molecules exhibit one and two more independent dissociation pathways with much energy being decayed via an extensive excitation of the bending modes of the parent molecules prior to the C-Br bond fission. This observation strongly suggests that the dissociation coordinate for the two carbon-chain branched molecules is no longer solely ascribed to the C-Br stretching mode but rather a combination of the bending-stretching modes.
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 photodis- sociation 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 3^Q0, 3Q1, and 1^Q1 states to the products （Br and Br^＊） were discussed. It is found that the nonadiabatic 1^Q1←3^Q0 transition plays an important role for Br photofragment in the dissociation of 2-C4HgBr 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 Ф（Br） decrease with increasing wavelength, the probability of curve crossing between 3 ^Q0 and 1^Q1 decreases with increasing laser wavelength.
