Ion-pair dissociation dynamics of HCl: fast predissociation.

We have studied the ion-pair dissociation dynamics of HCl --> Cl(-) ((1)S(0)) + H(+) in the 14.41-14.60 eV using tunable XUV laser and the velocity map imaging method. The measured ion-pair yield spectrum has P- and R-branch resolved vibrational structure, which indicates a predissociation mechanism for the ion-pair dissociation. All of the anisotropy parameters for the angular distribution of the fragments have the limiting values of beta = 2, which suggests that the predissociation occurs via (1)Sigma(+) Rydberg states, and is fast in comparison with the rotational period of HCl. To understand the predissociation dynamics, the diabatic potential energy curve of the ion-pair state has been calculated at the MRCI/CAS/vtz level. The experimental and theoretical results obtained in this work have provided a solid foundation for the previously proposed mechanism that the ion-pair dissociation occurs via predissociation of Rydberg states converging to HCl(+) (A(2)Sigma(+)).