Collisional quenching of CO B 1Σ+(v′=0) probed by two-photon laser-induced fluorescence using a picosecond laser

We report measurements of room-temperature, species-specific quenching cross sections of CO B (1)Sigma(+) (v' = 0) in collisions with He, Ne, H-2, N-2, Ar, CO, Kr, CH4, O-2, Xe, CO2, C3H8, and H2O. The measured quenching cross sections (in Angstrom(2)) were 0.25 +/- 0.02, 0.54 +/- 0.04, 11.0 +/- 0.4, 24.6 +/- 0.5, 27.7 +/- 0.5, 37 +/- 2, 42 +/- 2, 81 +/- 4, 85 +/- 5, 99 +/- 6, 133 +/- 5, 144 +/- 7, and 170 +/- 8, respectively. Two-photon excitation of the CO molecules via the Hopfield-Birge system (X (1)Sigma(+)-->--> B (1)Sigma(+)) was performed using the frequency-tripled 690 nm emission of a custom-built picosecond dye laser. Blue-to-green fluorescence in the Angstrom bands (B (1)Sigma(+)--> A (1)Pi) was detected using a microchannel-plate photomultiplier tube and recorded with a digital storage oscilloscope. The quenching cross sections were directly obtained by time resolving the temporal decay of the fluorescence signal and observing its variation as a function of the quencher pressure. The effect of radiative trapping on the observed fluorescence was also quantitatively modeled. (C) 2000 American Institute of Physics. [S0021-9606(00)02332-1].