Resonance-enhanced multiphoton ionization spectroscopy of X¹∑⁺ and a³II carbon monoxide using electron stimulated desorption as a source for rovibronically excited species

Electron stimulated desorption from CO monolayers chemisorbed on transition metal surfaces and from condensed CO layers were utilized as new sources for the production of nonthermal rovibrational distributions of CO probed by resonance-enhanced multiphoton ionization spectroscopy (REMPI). Highly vibrationally excited ground state CO molecules were studied by (l + l)-REMPI via the A ¹∏ and D′ ¹∑⁺ intermediate states, and metastable CO via the b ³∑⁺ and c ³∏ intermediate states. Rotationally resolved (1 + 1) spectroscopy via A ¹∏ (υ′≥20) allowed the verification of the intermediate term energies, including the existence of a potential barrier for the A ¹∏ state. (1+1) spectroscopy via D′ ¹∑⁺ is shown to provide the possibility to directly probe the D′ ¹∑⁺ potential curve. Additional spectral features accompanying the b ³∑⁺← a ³∏ (1+1) spectra which cannot be explained by known perturbations were found. In gas phase (2+1) spectroscopy via the B ¹∑⁺ and C ¹∑⁺ intermediate states, O- and S-branches could be detected even with linearly polarized light at very low CO densities (some 10^-6 Pa).