Observation of Rovibrational Transitions of HCl, (HCl)₂, and H₂O−HCl in Liquid Helium Nanodroplets

Abstract

We report the infrared spectra of HCl, (HCl)2, and H2O-HCl in liquid helium nanodroplets in the frequency region between 2680 and 2915 cm(-1). For the HCl monomer a line width of 1.0 cm(-1) (H35Cl) corresponding to a lifetime of 5.3 ps was observed. The line broadening indicates fast rotational relaxation similar to that previously observed for HF. For (HCl)2 the free HCl as well as the bound HCl stretching band has been observed. The nu2+ bands of (HCl)2 could be rotationally resolved, and rotational constants were deduced from the spectra. We observed both the allowed and the symmetry forbidden transition. However, the forbidden "broken symmetry" tunneling transition of the mixed dimer shows an intensity that is considerably enhanced compared to the gas phase. Upon the basis of the present measurements we were able to calculate the tunneling splitting in the excited state. The tunneling splitting is found to be reduced by 28% compared to the gas phase. Transitions from the ground state to the Ka=1 level of the free HCl stretch (nu1) are recorded and show considerable line broadening with a line width of 2 cm(-1). The excited state Ka=1 has an additional rotational energy of about 10 cm(-1), thereby allowing fast rotational relaxation by coupling to helium excitations. In addition we observed the HCl stretch of the HCl-H2O dimer, which exhibits an unusually large width (1.7 cm(-1) for H35Cl)) and large red shift (8.5 cm(-1)), compared to the gas-phase values. The large-amplitude motion originating from the libration mode of the HCl-H2O complex is supposed to act as a fast relaxation manifold.

Aggregation-Induced Dissociation of HCl(H 2 O) 4 Below 1 K: The Smallest Droplet of Acid

“…Bands of HCl monomer, HCl homodimer, and the undissociated HCl-H 2 O heterodimer in He droplets have been observed and assigned previously by us (39). In addition to those, we found two strong absorption bands centered at 2669.854(1) and 2667.804(2) cm −1 , subject to an intensity ratio of about 3:1 ( Fig.…”

Electronic spectroscopy of 9,10-dichloroanthracene inside helium droplets

“…In particular, line broadening, which is ascribed to inhomogeneous effects or fast relaxation processes, is rather subtle. 10,11 In contrast, numerous examples have been reported showing excessive line broadening in the electronic spectra of molecules when doped into helium droplets. 12,13 In Ref.…”

Communication: A new ab initio potential energy surface for HCl–H2O, diffusion Monte Carlo calculations of D and a delocalized zero-point wavefunction

“…4,23 A building block to understanding the clusters at the four-water limit and beyond is a detailed knowledge of even smaller HCl-H 2 O clusters, the first of which is the HCl-H 2 O dimer. The dimer, which is of great interest in its own right, has been firmly identified using a variety of techniques including velocity-map imaging with resonanceenhanced multiphoton ionization, 1, 2 infrared studies in liquid helium, 3,4,24,25 microwave spectroscopy, 26,27 ragout-jet FTIR 28,29 cavity ringdown spectroscopy, 30 and infrareda) Email: jmbowma@emory.edu matrix isolation spectroscopy. [31][32][33][34][35] Of these studies Refs.…”