| Summary: | 博士 === 臺灣大學 === 化學研究所 === 95 === Abstract
The photodissociation experiments of ICN and (ICN)2 are carried out with a home-built system. The state selected reactants and products can be investigated by using time-of-flight (TOF) mass spectroscopy coupled with resonance-enhanced multiphoton ionization (REMPI) techniques. A velocity map imaging (VELMI) detection is implemented to analyze speed and angular distributions of fragments in a high energy resolution.
Jet-cooled ICN molecules have been photodissociated at 277, 266, and 248 nm. Both ground state I (I≡2P3/2) and spin-orbital excited I* (I≡2P1/2) are detected by [2+1] REMPI, respectively. The corresponding branching ratio of I/I* is determined to be 0.75 ± 0.02, 1.22 ± 0.02, and 0.85 ± 0.1. The product anisotropic parameter, β, of I and I* are also obtained. For the main distribution of I products, β is estimated to be 1.25 ± 0.05, 1.31 ± 0.05, and 0.96 ± 0.05. For the main distribution of I* products, β is estimated to be 1.66 ± 0.1, 1.78 ± 0.1, and 1.86 ± 0.1. This strongly suggested that the ICN photodissociation at this range mainly result from the 3Π0+ parallel transition. In the mean time, the products with high internal energy are also observed. By considering previous results, I is mainly accompanied with the CN (X2Σ+) fragments in v”=0 at hot rotational temperature, whereas I* is produced with CN (X2Σ+) in v”=0 state but with cold rotational temperature. No hot vibrational CN fragment is observed at this
VI
wavelength range studied. At 266 nm the observed parallel transition ratio is 0.76. This value lies in between 0.85, reported by Houston et al, and 0.66, calculated by Morokuma et al.
We also investigated photodissociation of ICN dimer under jet-cooled condition using velocity map imaging technique. Because the neutral I2 molecules have been observed in the ICN dimer experiment, I+ was expected to originate from the photodissociation of neutral I2 or I2+. After carrying out the photodissociation experiment of I2+ ions via 2+1 REMPI from pure I2 sample, the total reaction pathways of ICN dimer photodissociation have been found. We also carried out the theoretical calculations to predict the geometry and energies of ground state and excited state of ICN dimer.
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