Vibrational relaxation of hydrogen by direct detection of electronic and vibrational energy transfer with alkali metals

A technique has been developed to measure the rate constant for vibrational relaxation of ${\mathrm{H}}_2^{\text{ν = 3,4}}$ by ${\mathrm{H}}_2^{\text{ν = 0}}$ . The technique uses a mechanically chopped, tunable, cw dye laser coincident with either of the Na resonance lines at 589.6 or 589.0 nm. Sodium vapor is contained in a glass cell along with Cs atoms and H₂. Sodium atoms, excited by the dye laser radiation, collisionally transfer electronic energy to H₂ producing some ${\mathrm{H}}_2^{\nu }$ . Only vibrational energy in ${\mathrm{H}}_2^{\nu }$ from levels ν = 3,4 can transfer to Cs as electronic energy and cause Cs resonance line emission at 894 and 852 nm. In this manner, using the observed emission as a detector of ${\mathrm{H}}_2^{\text{ν = 3,4}}$ , the vibrational relaxation rate constant was determined to be 3.9 × 10⁻¹⁴ cm³ sec⁻¹. Similar rate constants were measured, with somewhat less accuracy, for ${\mathrm{D}}_2^{\nu }$ colliding with D₂ and for ${\mathrm{H}}_2^{\nu }$ colliding with He. It was found that N₂, Na, and Cs also undergo electronic to vibration and vibration to electronic energy exchange.