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Coherent anti-Stokes Raman scattering is applied to the study of rovibrational populations in magnetic multicusp H2 and D2 discharges. This subject is of interest to negative hydrogen ion formation by volume plasma processes. The populations of high-lying rotational states (J≳5) in the vibrational levels v=0, 1, and 2 are found to be significantly higher than expected from the Boltzmann law. In H2 the net populations of the first four vibrational levels follow approximately the Boltzmann law, with the vibrational temperature of 2390 K (in a 90 V-10 A discharge at 55 μbar). In similar discharge conditions, the population of the state v=3 in D2 is higher than expected from the Boltzmann law. In the presence of the discharge a deficiency in H2 and D2 molecule density was observed and was attributed to the possible presence of H and D atoms. This was verified by an independent measurement of the atomic fraction and temperature. The density of negative ions, measured by the photodetachment technique, is also reported.

The rotational temperature of the excited state O2 (b1 Sigma g+, v=0) in an oxygen glow discharge is measured from the intensity distribution of the atmospheric A-band O2 (b1 Sigma g+, v=0) to O2(X3 Sigma g-, v=0) at lambda =760 nm. The kinetic temperature, often called the gas temperature is also deduced using vacuum ultraviolet absorption spectroscopy in the same experimental conditions: pressure p=0.5-5 torr, discharge current up to 100 mA and deposited power up to 2 W cm-1. It is shown that the rotational temperature of the A-band is equal to the rotational temperature of the molecular X3 Sigma g- ground state and of the first metastable as 1 Delta state measured by coherent anti-Stokes Raman spectroscopy. Since the kinetic temperature is in equilibrium with the rotational temperature of the ground state, we conclude that the rotational temperature of the O2 (b1 Sigma g+) state is identical to the gas temperature.

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For the first time, vibrational level population distributions of a low pressure D.C. flowing discharge were measured up to ν = 14 using Coherent Anti-Stokes Raman Scattering (CARS). The vibrational populations of the ground state N2(X 1Σ+g, ν) were obtained by recording rotationally resolved CARS spectra of the different vibrational bands. In the discharge region, the vibrational distributions have a non Boltzmann behaviour, as expected. The vibrational parameters were found to lie in the range 4 000-5 000 K, and rotational temperature to be about 550 K. Similar results were observed in the post-discharge region up to ν = 10. The vibrational and rotational temperatures were about 3 000 and 350 K respectively. The problems experienced while recording CARS spectra in low density media are discussed and comparisons with previously published theoretical models are presented