Study of Excitation Transfer in a Flowing Helium Afterglow Pumped with a Tuneable Dye Laser. II. Measurement of the Rate Coefficient for the Rotational Relaxation of He2(3p 3Πg)

The rotational relaxation of the He2(3p 3Πg) state is examined by optically pumping a flowing helium afterglow with a tuneable dye laser. The population of the J = 8 rotational state is enhanced by optically saturating the R7 component of the transition connecting this state with the metastable He2(2s3Σu+) molecular state. From the lifetime and yield of the Q7 component, the rate coefficient for the rotational relaxation via the forbidden ΔJ = 1 channel is determined to be of the order of 2× 10−11 cm3/sec. It is found that this represents about half of the total rate of rotational relaxation in this state.