Observation and spectroscopy of high-lying states of the CaOH radical: Evidence for a bent, covalent state

The CaOH radical has been produced in a supersonic molecular beam by the reaction of water vapor with laser desorbed calcium. Three new electronic states, the D 2Σ+, E 2Σ+, and F states have been observed by laser induced fluorescence and resonance enhanced multiphoton ionization spectroscopy. The D and E states are linear, but the F state is bent, the first bent and strongly covalent state of CaOH to be observed. Vibrational constants for the D state have been determined and a partially rotationally resolved spectrum has provided the rotational constant and Ca–OH bond length in this state. The D and E states are more strongly bound than the ground state, perhaps indicating some covalent contribution to the bonding. Additional vibrational constants of the ground electronic state including the CaO–H vibrational frequency have been determined from the emission spectra.