Predissociation mechanism and dynamics of HCP

In the present study, we have observed absorption, fluorescence excitation, and CP radical action spectra of the HCP molecule in the vicinity of the dissociation threshold to H((2)S) + CP(X (2)Sigma(+)). In addition, we have measured the rotational distribution of the CP radical produced from certain single rovibronic levels of the parent HCP molecule. It is found that the CP radical action spectrum starts to appear at the point where the fluorescence intensity decreases suddenly. On the basis of the precise energetic consideration between the parent and the product rovibronic energies, the dissociation energy of HCP to H((2)S) + CP(X (2)Sigma(+)) is determined to be 41 662.3 +/- 0.5 cm(-1). The energy distribution in the predissociation is found to be basically statistical; however, the prominent preferences in the rotational distributions or nonstatistical distributions are observed only when the vibronic energy of the parent level is smaller than the dissociation threshold energy. This preference is qualitatively interpreted by the inefficient energy transfer from the rotational to the vibrational degrees of freedom in the exit region of the X state potential energy surface. As a result, the dissociation proceeds along the linear H-C-P configuration, and this geometrical restriction makes nonstatistical rotational distribution of the CP radical.