Photodissociation and multiphoton ionization dynamics using two-dimensional photofragment imaging technique

Abstract

Photodissociation of $CF_3I$ at 277 nm: The photodissociation of $CF_3I$ cooled in a supersonic molecular beam has been investigated at 277 nor by state-selective photofragment imaging. Fragmented iodine atoms of two spin-orbit states are state-selectively ionized and projected onto a two-dimensional position-sensitive detector, to obtain their speed and angular distributions. The anisotropy parameter for an excited iodine atom $I^*(^2P1/2)$, $β(I^*)$, is found to be 1.83 and is consistent with a dissociation lifetime in the order of 150 - 350 fs from rotational correlation function. Contrary to earlier reports, the parallel-like distribution for the ground state iodine atom $I(^2P3/2)$ at this wavelength, shows a more favorable curve-crossing dissociation path (68%) from $^3Q_0$ to $^1Q_1$ and a less favorable direct dissociation path (32%) from $^3Q_1$. The recoil energy distribution of I is found to be broader than that of $I^*$ and is correlated with a variety of energy disposal channels by an e symmetry vibration at the crossing point. The results are compared with previous works, and the strong photon energy dependence of the energy partitioning in $CF_3+I^*$ channel and curve crossing are interpreted in terms of the final state interaction and curve crossing probability, respectively. Photodissociation of t-Butyl Iodide at 277 and 304nm: The photo-dissociation of $t-C_4H_9I$ has been studied at 277 and 304 nm in a supersonic molecular beam. The fragments (I and $t-C_4H_9I$ radical) are selectively ionized by resonance-enhanced multiphoton ionization and then projected onto a two-dimensional position-sensitive-detector to obtain their translational energy and angular distributions. The energy distribution is found to consist of three components - one Boltzmann and two Gaussian distributions. Their anisotropy parameters range from 0.5 to 1.7 and display the parallel transition characteristic, where the greater the kinetic energy of the component the strong...