Resonance multiphoton ionization study of theB1Σ+state of CO

Abstract

We report measurements of $(4+2)$ resonantly enhanced multiphoton ionization (REMPI) of CO. The excitation route is first to the $\ensuremath{\nu}=0$ level of the CO $B{}^{1}{\ensuremath{\Sigma}}^{+}$ state followed by the absorption of additional two photons to reach the ionization continua. Measurements of the ${\mathrm{CO}}^{+}$ and ${\mathrm{C}}^{+}$ ion intensities as a function of the wavelength were made, yielding no rotational structure of any intermediate resonant state in contrast to the $(2+1)$ REMPI experiment. In a second measurement, the laser frequency was set at the $\ensuremath{\upsilon}=0$ band head of the $B{}^{1}{\ensuremath{\Sigma}}^{+}$ and the kinetic-energy spectrum of the ejected electrons was measured. The observed photoelectron spectrum is assigned to the multiphoton ionization of CO via the resonant $X{}^{1}{\ensuremath{\Sigma}}^{+}$ to $B{}^{1}{\ensuremath{\Sigma}}^{+}$ excitation.