Correlated Photofragmentations

• Main Authors: Hsieh, Chi-Hsun, 謝奇勳
• Other Authors: Professor S.M. Lin
• Format: Others
• Language: en_US
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/14543633286200877190

博士 === 國立臺灣大學 === 化學研究所 === 88 === A simple, cost-effective method, which combines the commonly used state-selective REMPI detection technique with the core-sampling concept in high resolution ion velocity measurements, has been developed to investigate the quantum-state pair-correlation of the two photofragments and the vector properties of a photofragmentation process. Two examples for the study of the scalar pair-correlation and the vector correlations between the internal state distributions of the NO(v = 0, 1; J ) and O(3Pj=0,1,2) photofragments from the photodissociation of NO2 at 355 nm, and of the scalar pair-correlation between the internal state distributions of the SO(v = 0 — 5 ; J) and O(3Pj=0,1,2) photofragments via monitoring oxygen atoms O(3Pj) produced in 193 nm photodissociation of SO2 are presented for illustrations in this dissertation. Some important results are obtained. (1) NO2 @ 355 nm (a) The rovibrational distributions of the NO cofragments revealed by the time-of-flight (translational energy) measurement of the O(3Pj) fragment show clear j-dependence. And the strong correlation between the NO(v, j) distributions and fine-structure levels of O(3Pj) are manifested on the NO( v = 0 ) / NO( v = 1 ) ratio and NO( low j ) / NO( high j ) ratio in NO( v = 1 ) level. (b) The angular distribution of each individual fine-structure state of the O-atom also exhibits distinct correlation with the internal states of the counter NO fragment, which displays a downward trend with the increase in the rotational quantum numbers of the NO fragment. This velocity dependence of anisotropy parameter can be attributed to the bending mode excitations of the parent molecules ( NO2 ) during dissociation. (c) Strong orbital alignment is observed in O(3P1) photofragment which depends on the recoil velocity ( i.e. the internal state of NO cofragment ) and contains both incoherent and coherent excitations of the parent molecule. The possible dynamical implications will also be discussed. (2) SO2 @ 193 nm (a) The rovibrational distributions of the SO( v, J ) revealed by the time-of-flight (translational energy) measurement of each individual fine-structure state of the O-atom ( i.e. O(3Pj) fragments ) show clear j-dependence manifested near Et  1200 cm —1, which could be assigned as v = 4.