TEMPERATURE-DEPENDENCE OF HE(2 (3)P(J)) REACTIONS - COLLISION-INDUCEDMIXING AND CONVERSION TO HE2(B(3)PI(G)) MOLECULES

The rate coefficients for mixing between He(2 P-3(J,MJ)) levels during collisions with ground-state helium atoms and for conversion of He(2 P-3(J)) atoms to He-2(b 3PI(g)) molecules via three-body reactions in helium gas have been investigated over the temperature range 1.6-300 K . The measured rate coefficients for collisionally induced P-state mix ing decrease slowly with decreasing temperature, from (1.8 +/- 0.5) X 10(-9) cm3 s-1 at 300 K to (4.5 +/- 0.5) X 10(-10) cm3 s-1 at 4.2 K. T he rate coefficients for the production of He-2(b 3PI(g)) molecules vi a three-body reactions are observed to increase with decreasing temper ature and are described by the relation k(p) congruent-to (2.5 + 267T- 1) X 10(-32) cm6 s-1. This behavior, which is very different from that noted in earlier studies of the conversion of He(2 S-3(1)) atoms to H e-2(a 3SIGMA(u)+) molecules through three-body reactions, suggests tha t the reaction is not thermally activated.