CO dimer: the infrared spectrum revisited.

Area of Science:

• Molecular Spectroscopy
• Quantum Chemistry
• Chemical Physics

Background:

• The carbon monoxide (CO) dimer is a weakly bound complex.
• Understanding its vibrational and rotational states is crucial for molecular physics.
• Previous studies have identified some energy levels of the CO dimer.

Purpose of the Study:

• To investigate the infrared spectrum of the CO dimer in its excited vibrational state (vCO = 1).
• To identify and assign new rotational levels and intermolecular vibrational modes.
• To determine the magnitude of resonant vibrational splittings in different dimer isomers.

Main Methods:

• Broad-band infrared spectroscopy using a tunable quantum cascade laser.
• Probing a supersonic jet expansion at low rotational temperatures (~2.5 K).
• Analysis of spectral data, including combination differences, to assign rotational levels.

Main Results:

• Recorded the infrared spectrum of the CO dimer in the 2135-2200 cm(-1) range.
• Identified the first known excited state levels (vCO = 1) with A(+) symmetry.
• Assigned 28 new rotational level stacks (A(-) symmetry) for vCO = 1, extending up to 51 cm(-1) above the origin.
• Determined small resonant vibrational splittings (<0.2 cm(-1)) for both C-bonded and O-bonded isomers.
• Provided assignments for the first 13 stacks in terms of the geared bending intermolecular vibration.

Conclusions:

• The study provides a comprehensive analysis of the CO dimer's excited vibrational state.
• It reveals detailed information about rotational structures and intermolecular vibrations.
• The findings contribute to a deeper understanding of van der Waals complexes and their spectroscopy.