Low-Temperature Rotational Relaxation of N₂ in Collisions with Ne

Abstract

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.

Initial mechanisms for the unimolecular decomposition of electronically excited nitrogen-rich energetic salts with tetrazole rings: (NH4)2BT and TAGzT

“…The rotational transition signals of N 2 from TAGzT are much weaker, and only the strongest S 0 peak is identified, as other peaks are too close to the background noise. The rotational spectrum for the N 2 /He mixture and (NH 4 ) 2 BT expansions is similar to that of previous studies, indicating an N 2 rotational temperature of about 20 K. 16,17,[47][48][49][50] The N 2 signals from TAGzT are much less intense and, through the comparison to the N 2 gas spectra in different rotational temperatures in previous studies, 16,17,[47][48][49][50] the rotational temperature of the N 2 product released from the TAGzT salt is assigned as lower than 30 K.…”

“…a transitions] through time of flight mass spectrometry (TOFMS). [47][48][49] Note that the energetic salt sample is in a condensed phase ((NH 4 ) 2 BT and TAGzT trapped in an R6G matrix) under 532 nm laser ablation, while for the 283 nm excitation/decomposition processes, it is in the form of an isolated energetic molecule. The UV laser wavelengths for this process are generated by a dye laser, pumped by the second harmonic (532 nm) of a Nd: yttrium aluminum garnet laser's fundamental output (1.064 µm), in conjunction with a frequency doubling system.…”

“…The rotational temperature of the 3% N 2 mixture calculated from a Boltzmann plot equals 28 K. The rotational temperatures of N 2 decomposition products from (NH 4 ) 2 BT and TAGzT (as indicated) are estimated to be smaller than 30 K. Figure 5. [47][48][49] The rotational spectrum of N 2 from (NH 4 ) 2 BT clearly evidences two peaks of the S branch: S 0 and S 1 . The rotational transition signals of N 2 from TAGzT are much weaker, and only the strongest S 0 peak is identified, as other peaks are too close to the background noise.…”

“…The 283 nm excitation wavelength corresponds to the resonance (1-0) vibronic band of the a 1 Π g ← X 1 Σ g electronic transition of the N 2 product. [47][48][49] REMPI (2 + 2) rotationally resolved spectra of the N 2 product from the two energetic salts are obtained by scanning the laser excitation wavelength. The line width of the N 2 mass peak is 10 ns (∼laser pulse width) and laser beam intensity is varied without change in the N 2 TOFMS line width or spectral features.…”

Spatial distribution of the neutral gas temperature in rf and dc magnetron sputter discharges determined by fitting rotational spectra of the N2+ using a two-temperature fit

“…But one of the probably most used is the nitrogen molecule and its ion. The rotational level distribution of a certain electronic and vibronic state can be measured by several methods, among them optical emission spectroscopy (OES), laser-induced fluorescence, Raman scattering [17], Fourier-transformed infrared spectroscopy [4], resonance-enhanced multiphoton ionization [18] or broad-band mode-locked cavity-enhanced absorption spectroscopy [19]. Under certain experimental conditions the rotational temperature reflects the neutral gas temperature more reliably than the translational temperature measured by Doppler broadening [20].…”