ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
We have measured the terminal rovibrational distribution of Na2 in a molecular beam produced by a supersonic expansion of pure sodium at source pressure × nozzle diameter products p0d=0.02 and 0.32 Torr cm. The rovibrational distribution was determined by the laser-induced fluorescence technique and covers the 550–1200 and 550–2700 cm−1 internal energy ranges, respectively. The highest vibrational state for which molecules were detected is v‘=15. For the lower stagnation pressure, the internal energy distribution is well relaxed and can be described by a temperature of about 350–400 K. For the p0d=0.32 Torr cm experiment, the distribution is nonthermal with a large population excess for the levels with a high internal energy. The local temperature exceeds 460 K at 2000 cm−1. A striking result is that the rovibrational distribution depends almost exclusively on the internal energy (i.e., it does not depend much on the partitioning of this energy between vibration and rotation). This new result does not seem to be in contradiction with previous experiments which tested only a small set of levels. We discuss the mechanisms of the rovibrational relaxation during the sodium beam expansion. Recent experiments have shown that this relaxation is a very efficient process and we believe that it can explain our observations. We attribute the population excess of the rovibrational levels with a high internal energy to the process of dimerization in the expansion. Finally, a nonstatistical behavior of the Na2 ortho/para population was observed for the vibrational levels v‘=10–15. Such an effect for hydrogen molecules formed by three-body recombination has been predicted by Roberts within the resonance complex theory of this process [R. E. Roberts, J. Chem. Phys. 54, 1423 (1971)].
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.465860
