Spectra of CO2-N2 dimer in the 4.2 μm region: Symmetry breaking of the intramolecular CO2 bend, the intermolecular bend, and higher K-values for the fundamental.

Abstract

Infrared spectra of the CO2-N2 dimer are observed in the carbon dioxide ν3 asymmetric stretch region (≈2350 cm-1) using a tunable infrared optical parametric oscillator to probe a pulsed slit jet supersonic expansion. Previous results for the b-type fundamental band are extended to higher values of Ka. An a-type combination band involving the lowest in-plane intermolecular bending mode is observed. This yields a value of 21.4 cm-1 and represents the first experimental determination of an intermolecular mode for CO2-N2. This intermolecular frequency is at odds with the value of 45.9 cm-1 obtained from a recent 4D intermolecular potential energy surface. In addition, two weak bands near 2337 cm-1 are assigned to the CO2 hot band transition (v1, v2 l2, v3) = (0111) ← (0110). They yield a value of 2.307 cm-1 for the splitting of the degenerate CO2 ν2 bend into in-plane and out-of-plane components due to the presence of the nearby N2. The in-plane mode lies at a lower energy relative to the out-of-plane mode.