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 Na 2 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 153±5'K and a rotational temperature of 55 ± 10'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.

On Metal‐Atom Clusters IV. Photoionization thresholds and multiphoton ionization spectra of alkali‐metal molecules

“…Further window flanges are used for laser-induced fluorescence experiments [34]. Special optical components image the beam fluorescence on a photomultiplier tube (RCA 7265).…”

My Life with LIF: A Personal Account of Developing Laser-Induced Fluorescence

“…Adapted with permission from Reference 17. of the molecules (19). Figure 8 shows an example: Subsequent work by Sinha et al (20) would show that the Na 2 molecules are not randomly distributed in the flow but align with the stream direction, like logs flowing in a river.…”

Critical assessment: Use of supersonic jet spectrometry for complex mixture analysis (IUPAC Technical Report)

“…In this latter case, the velocity distribution is rather broad, even when molecular collisions are negligible. Supersonic jet cooling and spectral line narrowing were first reported for di-and tri-atomic molecules [2,3]. Since then, this technique has been extended to large molecules containing more than 20 atoms.…”

“…Thus, the density decreases in proportion to the square of the distance from the nozzle. The number density at the distance l from the skimmer placed at the distance X from the nozzle is further reduced by a factor of X 2 /(X + l) 2 . As a result, the sensitivity in supersonic jet spectrometry is substantially degraded in comparison with the case in non-jet spectrometry.…”