Intramolecular energy transfer between oriented chromophores: High-resolution infrared spectroscopy of HCl trimer

Abstract

Detailed dynamical and structural information has been obtained for hydrogen-bonded (HCl)(3) clusters via high-resolution IR laser absorption spectroscopy in a supersonic slit expansion. Multiple rovibrational bands in an approximate to3000 cm-1 HCl stretch region have been assigned and analyzed for H Cl-35/H Cl-37 isotopomeric contributions, corresponding to excitation of (i) the degenerate antisymmetric HCl stretch in isotopically pure (H Cl-35)(3), (ii) high- and low-frequency components of the nearly degenerate HCl stretch in H Cl-37 (H Cl-35)(2), (iii) the low-frequency component of the corresponding HCl stretch in (H Cl-37)(2) H Cl-35. The isotopically pure (H Cl-35)(3) results are in good agreement with earlier diode-laser efforts. A simple exciton model for vibrational coupling between HCl subunits is presented that indicates rapid intramolecular energy flow (beta approximate to-1.89 cm-1, tau approximate to 2.8 ps) in the trimer ring, which is in good agreement with vibrationally mediated tunneling rates observed in the HCl dimer. Spectral analysis at slit jet resolution indicates a Deltanuapproximate to120 MHz homogeneous line broadening and an excited-state lifetime of approximate to1.3 ns. The data is consistent with intramolecular vibrational redistribution-induced opening of the trimer followed by true predissociation to either (HCl)(2)+HCl or 3HCl on a longer time scale. (C) 2004 American Institute of Physics.