New Infrared Spectra of the Water−CO2 Complex: Determination of four Intermolecular Modes and test of a High-Level Potential Energy Surface

Abstract

High resolution infrared spectra of water - CO2 dimers are further studied using tunable infrared sources to probe a pulsed slit jet supersonic expansion. The relatively weak transition of D2O-CO2 in the D2O 1 fundamental region (~2760 cm-1), and that of D2O-13CO2 in the D2O nu3 region (~2786 cm-1), are observed for the first time. Combination bands involving the intermolecular in plane geared bend (disrotary) mode are observed for H2O-CO2 (~1642 cm-1) in the H2O nu1 region, for HDO-CO2 (~2761 cm-1) in the HDO nu3 region, and for D2O-CO2 (~2705 and 2821 cm-1) in the D2O nu1 and nu3 regions. In addition, a combination band involving the intermolecular twist (internal rotation) mode is observed for D2O-CO2 (~2874 cm-1) in the D2O nu3 region. This twist transition actually appears as two bands of similar intensity, separated by 2 cm-1, suggesting the “accidental” near-coincidence of the “real” combination state with a “dark” background state of the same symmetry. Intermolecular mode frequencies determined from the combination bands are in very good agreement with a recent theoretical calculation based on a high level ab initio potential surface