Light-induced shifts in chemical equilibria: Optical orientation-induced shift in 2Li(g)↔Li2(g) and o r t h o/p a r a enrichment

The shift in the equilibrium distribution between reactants and products in the chemical reaction 2Li⇋Li2 that accompanies an optical orientation of the atomic Li spin angular momentum has been observed, and its dependence and degree of atomic orientation is reported. An examination of the resolved rotational structure in the Li2 electronic spectrum reveals the production of molecular nuclear spin polarization that accompanies the equilibrium shift, resulting in a change in the ortho/para ratio for Li2. Orientation of the spin angular momentum of the 2 2S1/2 ground state Li atoms was produced in a vapor cell by optical pumping with a tunable, single mode cw dye laser, and the molecular density in different rotational states of the 7Li2 X 1Σ+g (v=0) molecular state was monitored using a second cw dye laser.