Laser fluorescence studies of molecular iodine

We have studied quantitatively the circular polarization of rotationally resolved features in the laser-induced fluorescence from I2 excited by the 5145 Å argon laser line, and its variation with various experimental parameters such as light intensity, iodine and foreign gas pressure. Optical pumping of the ν″ = 0, J″ = 13 level of 1Σ g + has been unambiguously demonstrated and the variation of C with gas pressure has been analysed to yield cross sections for elastic and inelastic collisions which relax the oriented ground state. Experiments on the dipolar array of oriented 3Π0u + molecules at very high pressures show that the circular polarization ratio does not change under conditions of many gas kinetic collisions per lifetime. This indicates that a selection rule ΔM = 0 operates on elastic collisions of I2* with other atoms and molecules, which appears to be rigorously adhered to.