Spectroscopic Studies of Unimolecular Reaction Dynamics of Vibronically State-selected Molecules

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In order to investigate vibrational dynamics of vibronically state-selected acetylene, various spectroscopic techniques have been applied.(1) The rovibronic level system of the ungerade nv_3'+v_4'/v_6' (n=0,1,2,3) vibrational states in the A^1A_u state of acetylene which are accessible from the selected rotational level J" of the v_3" state in the X^1Σ_g^+ state. The nv_3'+v_6' and nv_3'+v_4' state are found to couple with each other by the a-and b-axis Coriolis interactions.(2) Most of rotational levels of the 3v_3'+v_6' state split into two or more levels, while those of the 3v_3'+v_4' state are single. The fluorescence decay from the spilit levels shows a quantum beat under a weak magnetic field. This indicates that the level splitting is attributable to the S-T interaction. Since the v_6' mode is in-plane while the v_4'is out-of-plane, the S-T interaction occurs in the planar geometry of the excited acetylene.(3) The H-atom action spectroscopy has been applied to investigate the predissociation efficiency of acetylene excited in the gerade vibrational states in the region of 47000〜50600 cm^<-1>. The predissociation is enhanced in the states exceeding the inversion barrier of the bending vibration which is located around 48000 cm^<-1>.