Ground state relaxation measurements by laser-induced depopulation

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Abstract
We have directly measured the repopulation rate for an individual rotational level in the electronic ground state of a homonuclear molecule. A pulsed dye laser was used to depopulate (v″, J″) level of Na2 by pumping a transition of the form (v′, J′) ← (v″, J″) in the B1Πu‐X1Σ+g blue–green band system. The (v″, J″) state was repopulated by collisions with other sodium species and with an argon buffer gas. The transmission of a second, delayed, pulsed dye laser was monitored, serving as a probe of the (v″, J″) state’s population at various delay times. The argon pressure was varied and the procedure repeated. The Na2–argon collision cross section may also be determined by this method.