Isotope effect in multiphoton ultraviolet photolysis of CO

Abstract

Two‐photon dissociation of carbon monoxide near 193 nm with a tunable ArF* laser to yield excited C(2 ¹D) atoms is reported. The atoms are detected by subsequent absorption of a third laser photon to C(3 ¹P°) followed by emission of 248 nm fluorescence to C(2 ¹S). The process is found to be isotopically sensitive; the C(2 ¹D) yield from ¹³C ¹⁶O and ¹²C ¹⁸O is a factor of 6 greater than from ¹²C ¹⁶O. The isotope effect is attributable to an enhancement in the two‐photon matrix element due to the shift in the near resonant a ²Π, v=2 intermediate state. C₂ Swan band emission is also observed, arising from association of the free carbon atoms, and exhibits a corresponding isotope effect. Finally, collisional processes are observed involving excited carbon atoms and electrons, using two‐photon ionization of a small quantity of added xenon atoms as a new technique for producing a controlled density of free electrons.