Zero-Field Level-Crossing Spectroscopy of theAΠ1State of Carbon Monoxide

Level-crossing measurements have been made on the $A{}_{}{}^1{}_{}{}^{}\Pi$ state of CO by observing the fluorescence of resolved rotational features of the (1,0) and (2,0) bands of the fourth positive system in a magnetic field. Each of the rotational features studied is comprised of three unresolved lines, one each from the $P$, $Q$, and $R$ branches of the system. The field-dependent part of the fluorescence consists of a superposition of three Lorentz curves which have halfwidths proportional to $g_{J^{\prime }}{\tau }_{J^{\prime }}$, the product of the Lande $g$ factor and the lifetime of the state. The relative contributions of each line to the level-crossing signal are evaluated by simulating spectra which reproduce both the band spectrum of the lamp used for excitation and the spectrum of the fluorescence. Lifetimes of the vibrational levels are obtained by assuming that the $g$ factors can be computed from the case (a) coupling scheme for unperturbed rotational states and then finding the value of ${\tau }_{J^{\prime }}$ which produces the best fit to the data. The results from the present work are $\tau (v^{\prime }=1)=10.4\mathrm{}\pm 0.8$ nsec, $\tau (v^{\prime }=2)=8.5\mathrm{}\pm 1.0$ nsec. Data from the $J^{\prime }=22\mathrm{}$ to $J^{\prime }=25\mathrm{}$ rotational states of the $v^{\prime }=1\mathrm{}$ level clearly show the effects of the perturbation which couples the $a^{\prime }{}_{}{}^3{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$ and the $A{}_{}{}^1{}_{}{}^{}\Pi$ states. The averaged result for the matrix element which couples the two states is found to be $\delta =2.7\mathrm{}\pm 0.9$ ${\mathrm{cm}}^{-1\mathrm{}}$.