Quantum state distributions of HCl from the ultraviolet photodissociation of HCl dimer

The rovibrational state distributions for the HCl product of the 193 nm pho todissociation of (HCl)(2), (HCl)(2)+h nu -->H+Cl+HCl, have been measured. The HCl dimer is prepared in a supersonic expansion of HCl in Ar, and its p hotoproduct detected by resonant multiphoton ionization under collisionless conditions. The state distributions are extremely "cold," with very little of the available energy deposited in either rotation or vibration of the s urviving HCl molecule. Only v(')=0 product is observed, and linear rotation al surprisal analysis yields an extremely large surprisal parameter, theta (r)' of 95(8). The results are in excellent agreement with theoretical pred ictions. (C) 2001 American Institute of Physics.