Collisional quenching of He/sub 2/ molecules in the a /sup 3/. sigma. /sup +//sub u/ level by impurity gases

Measurements in a fast pulsed discharge of the room temperature rate constant for the quenching of He/sub 2/ molecules in the metastable a /sup 3/..sigma../sup +//sub u/ level by Ar, N/sub 2/, O/sub 2/, H/sub 2/, and CO/sub 2/ are reported at He pressures of 200 and 300 Torr and for various pressures of the impurity gas. The concentration of He/sub 2/ molecules in the a /sup 3/..sigma../sup +//sub u/ level is monitored by using a pulsed dye laser to excite the Q5 line of the e /sup 3/..pi../sub g/reverse arrowa /sup 3/..sigma../sup +//sub u/ transition and by observing the subsequent d /sup 3/..sigma../sup +//sub u/..-->..b /sup 3/..pi../sub g/ fluorescence. The results for N/sub 2/, Ar, and CO/sub 2/ are combined with previous data of others to obtain both bimolecular and termolecular rate constants for the quenching of the a /sup 3/..sigma../sup +//sub u/ level.