Selection of photodissociation products using a laser phase control techique.

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In this research, the laser phase control of product branching in photodissociation processes was investigated. In 1996, the ion imaging system was constructed, which enabled us to measure the translational enegies of the photofragments in the specific electronic, vibrational and rotational states. In this system, the photofragments were ionized using a resonance-enhanced multiphoton ionization technique. The producted ions were accelerated by an electric field and transferred in a field free drift tube. Then, the clouds of the spread ions due to the translational their motions were detected by a 2-dimensional detector. In 1997, the photodissociation processes of zone and CH_3 molecules were studied using the ion imaging system for the photodissociation products. The O (^3P) and O(^1D) atoms produced by the photodissociation of zone molecules in the Hartley and Huggins bands around 280-320nm were monitored. The photofragment excitation (PHOFEX) spectra for the O (^3P) and O(^1D) products were measured by scanning photodissociation laser wavelength and monitoring the signal intensities of O (^3P) and O (^1D) atoms. There were two dissociation pathways, O (^3P)+O_2 (X^3SIGMA^-_g) and O (^1D) +O_2 (a^1DELTA_g), in this photodissociation wavelength range. The PHOFEX spectrum for the O (^1P) atoms was found to have discreet vibrational structure of ozone, while that for the O (^1D) atoms were smooth. This indicated that the product branching was affected by the vibrational motion in the upper electronic surface of ozone, and suggested that the branching might be controlled by the laser coherent phase. For the CH_3I molecules, the effects of the phase difference between the one-photon and two-photon excitation processes were studied by monitoring the ion images of I^+ with 308 and 616nm laser light.