Communication: A rotationally resolved (2OH) overtone band in the water dimer (H2O)2

Abstract

Cw-CRDS spectra of water-rare gas supersonic expansions were recorded between 7229 and 7262 cm-1. The effective absorption pathlength was about 1 km in jet-cooled gas and the resolution about 1 × 10-4cm-1. Many well-resolved structures are observed that could be assigned from experimental evidence to H2O-Ar/Kr bands. Eight broader unresolved features are more specifically reported and assigned to small H2O multimers, in good agreement and refining previous observations by Nizkorodov et al. [J. Chem. Phys. 122, 194316 (2005)]. Among these, the band at 7256.5 cm-1is shown to be a Q branch of the water dimer with accompanying R and very weak P lines. The band is assigned to a Ka= 0 → 1 transition and rotationally analyzed, leading to a restricted set of upper state rotational constants. The upper state lifetime (60 ± 3 ps) is extracted from the linewidths.