Breaking symmetry with hydrogen bonds: Vibrational predissociation and isomerization dynamics in HF-DF and DF-HF isotopomers.
J T. Farrell, M A. Suhm, David Nesbitt
High-resolution near-IR spectra of jet-cooled HF-DF and DF-HF isotopomers are presented and analyzed for fundamental excitation in the HF (3870 cm-1-3960 cm-1) and DF (2840 cm-1-2880 cm-1) stretching region, based on direct absoption of tunable IR difference frequency radiation in a slit-jet supersonic expansion (10 K). Excitation spectra are obtained for all four stretching modes (*HF-DF, HF-*DF, *DF-HD and DF-*HF, where * denotes the vibrationally excited subunit), which probe both the hydrogen/deuterium bond donor and acceptor moieties in the complex. Vibrational redshifts and predissociation broadening measurements are compared with full 6-D quantum calculations on theoretical HF dimer potential surfaces, which indicate qualitative agreement with experiment. Each of the DF stretch-excited bands are well fit by conventional high-resolution rotational analysis to spectroscopic precision (Δ}υless than or equal to}0.0002 cm-1), whereas each of the corresponding HF stretch bands appear extensively perturbed (Δ}υless than or equal to}0.01 cm-1. This clear H/D isotope effect is the result of vibrational state mixing of the HF stretch-excited species with the manifold of combination band states built on DF-stretch excitation, and vibrational state mixing of the HF stretch-excited specites with the manifold of combination band states built on DF-stretch excitation, and therefore corresponds dynamically to intermolecular energy flow in the complex. Such vibrational state mixing is further corroborated by observation and analysis of dark state transitions that result from the K=1 manifold of HF*-DF interacting with the K=1 manifold of the vibrationally promoted isomerization over the tunneling barrier, and yield a spectroscopic measure of the difference in hydrogen bond dissociation energies (Δ}Do=74.8(5)cm-1) for the two insotopomers.
, Suhm, M.
and Nesbitt, D.
Breaking symmetry with hydrogen bonds: Vibrational predissociation and isomerization dynamics in HF-DF and DF-HF isotopomers., Journal of Chemical Physics
(Accessed February 28, 2024)