Imaging H₂O Photofragments in the Predissociation of the HCl−H₂O Hydrogen-Bonded Dimer

Abstract

The state-to-state vibrational predissociation (VP) dynamics of the hydrogen-bonded HCl-H(2)O dimer was studied following excitation of the dimer's HCl stretch by detecting the H(2)O fragment. Velocity map imaging (VMI) and resonance-enhanced multiphoton ionization (REMPI) were used to determine pair-correlated product energy distributions. Following vibrational excitation of the HCl stretch of the dimer, H(2)O fragments were detected by 2 + 1 REMPI via the C (1)B(1) (000) ← X (1)A(1) (000) transition. REMPI spectra clearly show H(2)O from dissociation produced in the ground vibrational state. The fragments' center-of-mass (c.m.) translational energy distributions were determined from images of selected rotational states of H(2)O and were converted to rotational state distributions of the HCl cofragment. The distributions were consistent with the previously measured dissociation energy of D(0) = 1334 ± 10 cm(-1) and show a clear preference for rotational levels in the HCl fragment that minimize translational energy release. The usefulness of 2 + 1 REMPI detection of water fragments is discussed.