Beschreibung:
<jats:p>We report a detailed study on the IR spectroscopy of HCl-water complexes in superfluid helium nanodroplets in the frequency range from 2660 to 2675 cm−1. We have recorded spectra of \documentclass[12pt]{minimal}\begin{document}${\rm HCl-H}_2^{16}$\end{document} HCl −H216O as well as of \documentclass[12pt]{minimal}\begin{document}${\rm HCl-H}_2^{18}$\end{document} HCl −H218O complexes and compared these results with theoretical predictions. In addition, we have carried out mass-selective intensity measurements as a function of partial pressure of HCl as well as of \documentclass[12pt]{minimal}\begin{document}${\rm H}_2^{18}$\end{document}H218O (pick-up curves). The results support a scenario where the IR-absorption in this part of the spectrum contains contributions from undissociated as well as from dissociated clusters with Cl−(H2O)3(H3O)+ being the smallest dissociated complex. These findings are corroborated by additional electric field measurements yielding the orientation of the vibrational transition moment with respect to the permanent dipole moment. As a result we are able to assign a broad absorption band starting at 2675 cm−1 to dissociated HCl-water clusters (HCl)1(H2O)n with n ⩾ 4. The two narrow absorption lines at 2667.9 cm−1 and 2670 cm−1 are assigned to an undissociated cluster, in agreement with previous studies.</jats:p>