Internal state distribution of alkali dimers in supersonic nozzle beams

Abstract

By spectroscopically analyzing the white light and laser‐induced fluorescence excited in a nozzle beam of Na₂ molecules, we have measured the population distribution of the (v,J) levels of the ground state. The Na₂ molecules are produced in nozzle beams with various stagnation pressures (50–240 torr) of alkali metal and with nozzles of different throat diameters (0.12–0.50 mm). We find at a stagnation pressure of 50 torr and a nozzle diameter of 0.5 mm a Boltzmann distribution characterized by a vibrational temperature of $\text{153 ± 5°}\mathrm{K}$ and a rotational temperature of $\text{55± 10°}\mathrm{K}$ . Beams under different stagnation conditions have essentially the same internal state distribution. Studies of K₂ dimers produced in a nozzle beam with various stagnation pressures (20–300 torr) and a 0.25 mm nozzle throat diameter also show cooling in both vibrational and rotational modes. A search is made for atomic fluorescence arising from the photodissociation of dimers in high vibrational levels of the ground state. No evidence is found for the presence of vibrationally‐excited dimers in the nozzle beam.