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The characteristics of a commonly used pulsed valve for the production of free jets and molecular beams are analyzed in detail. Special attention is paid to the formation of gas pulses providing a quasisteady flow during a certain time interval within the pulse duration, and to the estimation of a scaling parameter (effective diameter) for the description of the flow field. The adequacy of this effective diameter is checked by performing time-of-flight measurements on molecular beams of Ne, N2, and CH4, and stimulated Raman spectra on free jets of N2 and CH4. © 1995 American Institute of Physics., Financed by the DGI-CYT of Spain under Grants No. PB91-0128 and No. PB92-02194.203.

9 pags., 5 figs., In this work several lines of the v3 fundamental band of the CH3 radical have been detected in a refrigerated hollow cathode discharge multipass cell filled with CH4, by using a discharge and laser amplitude double modulation technique, with a difference frequency laser spectrometer and a double phase sensitive detection. Bands of the precursor CH4 and of C2H4 and C2H6 produced in the discharge have been observed too. By Doppler broadening and absorption variations, the increase of temperature with the establishment of the discharge has been tested. It is only ∼15°C. Nevertheless, a very high sensitivity in transmittance variations with temperature is achieved for transitions from highly excited levels of stable species. The method proposed can be very useful for the assignment of very weak bands. © 1994 American Institute of Physics., This work was made with the financial support of the Spanish CICYT (Projects Nos. PB89-0041 and PB91-0128).

Neutral CH3 radicals in a hollow cathode discharge cell containing methane have been detected with a quadrupole mass spectrometer, using the threshold ionization technique. With the experimental conditions employed in this work the measured efficiency in CH3 production has been 0.2%, which is higher than that shown for other types of discharges in the bibliography. On the other hand a high depletion of the CH4 density has been observed and the mass spectrum of the discharge shows the appearance of compounds at m=25, 26, and 27, proceeding from recombination processes. ©1992 American Institute of Physics, Support of the Spanish CICYT (projects PB89-0041 and PB87-0273).