Experimental detection of rotational non-Boltzmann distribution in supersonic free molecular nitrogen flows

Abstract

In the present study, we measure the rotational population in supersonic nitrogen-free jets using a resonantly enhanced multiphoton ionization (REMPI) method [Chem. Phys. Lett. 115, 492 (1985)], which is not influenced by secondary electrons, unlike the electron beam method. Nitrogen ions are detected as a REMPI signal and its spectra, depending on the wavelength of an irradiated laser beam, are analyzed to measure rotational temperature through the Boltzmann plot. Nitrogen gas expands into a vacuum chamber from a sonic nozzle with a D=0.50mm diameter, setting P0∙D (where P0 is the source pressure), depending inversely on the nozzle Knudsen number, at 15Torrmm or lower. For P0∙D=15Torrmm, the rotational temperature distribution along the centerline of the jet, measured by using only the linear portion of the Boltzmann plot lying at smaller rotational quantum numbers, coincides with Marrone’s data [Phys. Fluids 10, 521 (1967)] measured by electron beam fluorescence, and the rotational relaxation rate ZR calculated by the relaxation equation results in 1.3. However, the non-Boltzmann rotational distribution appears evidently in supersonic free molecular nitrogen flows for P0∙D⩽15Torrmm, in good agreement with the simulation results of the combination of the classical trajectory calculation and the direct simulation Monte Carlo method by Koura [Phys. Fluids 14, 1689 (2002)]. As a decrease in P0∙D, the deviation from the Boltzmann distribution and the partial freezing of the population arise more upstream.

Modeling of carbon dioxide condensation in the high pressure flows using the statistical BGK approach

“…Statistical ESBGK method was used to simulate the flow of nitrogen through the nozzle. Results obtained from the simulations were compared with the experimental work of Mori et al, 33 who measured the rotational energy distributions in supersonic free jets of nitrogen using a resonantly enhanced multiphoton ionization (REMPI) method. The REMPI method enables the precise determination of the rotational energy distribution of highly rarefied gas flows as compared with other methods such as electron beam fluorescence (EBF).…”

Simulation of homogeneous condensation of small polyatomic systems in high pressure supersonic nozzle flows using Bhatnagar–Gross–Krook model

“…I in the 2D axisymmetric DSMC code, SMILE. 29 We used a time step of 1 × 10 −9 s, which is smaller than the local mean collision time, and ∼15 million simulated particles, each of which represented 1 × 10 9 gas molecules. We employed the new weighting scheme presented in Sec.…”

“…25-27. In our previous work, 26-28 the statistical ES-BGK method was implemented in the SMILE (Ref. 29) DSMC computational tool. A comparative study of the benchmark DSMC and statistical ES-BGK methods was carried out in Ref.…”

MEASUREMENTS OF ISOTOPE EFFECTS IN THE PHOTOIONIZATION OF N 2 AND IMPLICATIONS FOR TITAN'S ATMOSPHERE

“…This mixture then underwent supersonic expansion to form a molecular beam. Although the temperature of the beam was not measured directly, experiments done under similar conditions have yielded N 2 translational and rotational temperatures of 50 K (e.g., Aoiz et al 1999;Mori et al 2005), and little vibrational excitation is expected under these conditions; thus the N 2 beam was translationally, rotationally, and vibrationally cold. The beam was then crossed at 90…”