Studies On Photodissociation Dynamics Of HNCO Via NH(a~1Δ) +CO(X~1Σ~+) Channel

In this thesis, the photodissociation dynamics of HNCO was studied on singlet potential surface. The time-sliced ion velocity imaging technique and resonance enhanced multiphoton ionization (REMPI) are used to detect NH(a1Δ) products that formed in NH(a1Δ)+CO(X1Σ+) channel for the photodissociation of HNCO. Product translational energy distributions and angular distributions have been obtained by analysis of product ion imaging.In this work, the photolisis wavelengths were used mainly below 231 nm(-43290 cm-1). When the photolysis wavelength is 193 nm, levels up to v= 4 were observed for CO products. And a bimodal rotational distribution of CO(v= 1) was observed, speculating that it derived from two different dissociation pathways in the S1 state. When the photolysis wavelength range on 221-213 nm, the trimodal rotational distributions of CO(v=0) was found for a part of 1NH(v= 0 | j) products. The phenomenon was caused by potential surface interference effect. When the photolysis energies near the threshold to NH(a1Δ)+CO(X1Σ+) channel, the barrier on S1 was estimated range on 410～520 cm-1. And after exceeding this barrier, direct dissociation on S1 will quickly dominate. In addition, a part of the product signal was found not compatible in terms of energy conservation with the formation of 1NH+CO channel following electronic excitation from the ground vibrational state of HNCO(So) near the threshold. This part of the signal was derived from vibrational excitation of the parent HNCO(v5=1) molecules. The vibrational excited HNCO (v5=1) molecules also have the same barrier height as the ground state HNCO molecules, which can direct dissociation on S1 after exceeding this barrier.Through the systematic experimental study, the dissociation mechanism of HNCO via NH(a1Δ)+CO(X1Σ+) channel and the coupling relationship between the potential energy surface were explained on photolysis wavelength less than 231 nm.