Low-temperature rotational relaxation of N2 in collisions with Ne

22 pags.; 4 figs.
The rotational relaxation of nitrogen molecules in collisions with neon has been studied in supersonic expansions. N2 rotational temperatures have been determined from resonance-enhanced-multiphoton-ionization (REMPI) spectra performed in a series of supersonic molecular beams of N2 diluted in Ne. Terminal flow velocities and translational temperatures for the two expansion partners have been obtained from mass-selected time-of-flight measurements. From the measured data, the approximate isentropic behavior of the expansion could be verified and the thermal cross section for N2/Ne rotational relaxation at very low temperatures could be derived. The cross section increases from a value of ≈35 Å2 at 5 K, goes through a maximum of about 55 Å2 between 10 and 20 K, and then decreases smoothly to ≈25 Å2 for T = 60 K. The relaxation cross section for N2/Ne collisions is larger than that for N2/N2 collisions below roughly 20 K and smaller above this temperature. © 2001 American Chemical Society
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