The hydroxyethynyl radical (CCOH): an accessible isomer of the ketenyl radical (HCCO)?

The two lowest-lying states (X̃ 2A′′ and à 2A′) of the hydroxyethynyl radical (CCOH), an isomer of the ketenyl radical (HCCO), have been investigated theoretically using ab initio electronic structure theory. The ground and first excited electronic states of CCOH were determined to have trans-planar bent structures. At the TZ3P(2f,2d) CCSD(T) level of theory the two lowest-lying states of CCOH were predicted to lie 54.2 kcal/mol (2.35 eV, 19000 cm−1) and 65.8 kcal/mol (2.85 eV, 23000 cm−1) classically above the ground state of HCCO. Due to its large dipole moments and significantly large vibrational infrared (IR) intensities, the CCOH radical may be suitable for microwave and IR spectroscopic investigations.