The millimeter-wave spectrum of the normal isotope of the CO dimer, (12C16O)2, has been systematically surveyed in the regions 75-105 and 131-174 GHz, with additional measurements covering the entire 60-176 GHz range. By combining these results and using the technique of combination differences based on previously known energy levels, 14 new rotational levels have been assigned and precisely (≈0.1 MHz) located. They belong to 3 completely new states, 1 with A+ symmetry and 2 with A− symmetry. The position of the lowest energy A− state results in a new and lower value for the effective tunneling splitting of the CO dimer, 3.73 cm−1. The observation of dramatically different intensities for different bands supports the concept of two isomeric forms for (CO)2, the ground state having a larger intermolecular separation (≈4.4 Å) with most likely a C-bonded configuration, and the low-lying (0.88 cm−1) excited state having a smaller separation (≈4.0 Å) and an O-bonded geometry.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Physical and Theoretical Chemistry