Spectra of the D2O dimer in the O-D fundamental stretch region: vibrational dependence of tunneling splittings and lifetimes

TL;DR

This study investigates the vibrational dependence of tunneling splittings and lifetimes in the D2O dimer's O-D stretch region using high-resolution spectroscopy, revealing detailed vibrational effects on tunneling dynamics and lifetimes.

Contribution

It provides detailed experimental data on tunneling splittings and lifetimes in the D2O dimer's vibrational states, including excited states and mixed isotopologues, with high spectral resolution.

Findings

Tunneling splittings decrease in excited states.

Lifetimes vary from 0.2 to 5 nanoseconds depending on vibrational state.

Observation of a tentative combination mode involving intramolecular and intermolecular vibrations.

Abstract

The fundamental O-D stretch region (2600 - 2800 cm-1) of the fully deuterated water dimer, (D2O)2, is studied using a pulsed supersonic slit jet source and a tunable optical parametric oscillator source. Relatively high spectral resolution (0.002 cm-1) enables all six dimer tunneling components to be observed, in most cases, for the acceptor asymmetric O-D stretch, the donor free O-D stretch, and the donor bound O-D stretch vibrations. The dominant acceptor switching tunneling splittings are observed to decrease moderately in the excited O-D stretch states, to roughly 75% of their ground state values, whereas the smaller donor-acceptor interchange splittings show more dramatic and irregular decreases. Excited state predissociation lifetimes, as determined from observed line broadening, show large variations (0.2 to 5 nanoseconds) depending on vibrational state, K-value, and tunneling symmetry. Another very weak band is tentatively assigned to a combination mode involving an intramolecular O-D stretch plus an intermolecular twist overtone. Asymmetric O-D stretch bands of the mixed isotopologue dimers D2O-DOH and D2O-HOD are also observed and analyzed.