Electronic spectroscopy of the C state of NO by laser multiphoton ionization: Rotational structure of the C²Π (v′ = 0) ← X²Π (v″ = 0) two-photon band

Rotationally resolved two-photon electronic spectra of nitric oxide (NO) on the C²? (v' = 0) ? X²? (v? = 0) transition have been recorded in the near-UV between 384nm and 375nm by the (2+1) REMPI technique. The REMPI spectra of the d(0,0) band have been measured and assigned for jet-cooled NO, NO at room temperature and for the nascent, highly rotationally excited NO formed by the UV-photodissociation of nitrosyl chloride (CINO) in a one-colour dissociation-probe experiment. The wavelengths of all major rovibronic transitions have been measured accurately using optogalvanic spectroscopy and interference fringe counting as a calibration technique. The unperturbed transitions have been fitted to term values up to J = 53.5 with rotational energies in excess of 4000cm^-1 to a single algebraic energy formula. The absence of certain ?-doubled sub-branches in the spectra has been explained by different virtual two-photon routes via the electronic A state as the intermediate level. In connection with a discussion of two-photon parity selection rules and rotational line strengths we have shown that (2 + 1) REMPI spectroscopy of the C ? X transition on the d(0, 0) band will permit convenient and reliable measurements of the rotational and fine-structure populations of most, if not all levels of NO X (v = 0).