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

TL;DR

This study investigates the infrared spectra of the CO2-N2 dimer, revealing symmetry breaking in intramolecular and intermolecular bending modes, and providing new experimental data on intermolecular frequencies and mode splitting.

Contribution

The paper extends previous spectral analysis of CO2-N2 to higher Ka values and reports the first experimental measurement of an intermolecular mode, highlighting discrepancies with theoretical potential energy surfaces.

Findings

Observed a-type combination band with 21.4 cm-1 intermolecular frequency.

Detected hot band transition with 2.307 cm-1 splitting of CO2 bend.

Identified symmetry breaking effects in bending modes.

Abstract

Infrared spectra of the CO2-N2 dimer are observed in the carbon dioxide nu3 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 nu2 bend into in-plane and out-of-plane components due to the presence of the nearby N2. The in-plane mode lies at lower energy relative to the out-of-plane mode.