Reaction cross sections and rate constants for the D + H 2 (V ) 0-1, j ) 0-7) reaction have been obtained by quasi-classical trajectory (QCT) calculations on the three ab initio potential energy surfaces (PESs) available for this system. A good agreement has been found between the QCT and quantum mechanical (QM) reaction cross sections and rate constants for the D + H 2 (V ) 0-1, j ) 0) reactions. Thermal rate constants for the D + n-H 2 (V)0) and D + n-H 2 (V)1) have been calculated from the excitation functions, over a wide range of temperatures. The comparison with the quantum mechanical (QM) calculations and experimental results shows that, in general, QCT thermal rate constants are smaller than their QM and experimental counterparts, and this can be traced back to a decrease in the classical reactivity in the threshold region with rotational excitation of the reagents. In addition, the analysis of the QCT results provides an explanation for the differences found in thermal rate constants calculated on the three PESs in terms of specific features of each of these potentials.

The rotational relaxation of molecular nitrogen has been investigated down to temperatures of about 5 K with a combination of resonance-enhanced multiphoton ionization and supersonic beam time-of-flight techniques. The average rotational relaxation cross section obtained shows a maximum value of 50−60 Å2 at 20−30 K. For lower temperatures this cross section decreases and reaches a value smaller than 30 Å2 at T ≈ 5 K. For temperatures above 30 K, the cross section decreases slowly as the temperature grows and converges approximately to the determinations from other non-jet techniques and theoretical estimates available for T > 80 K. The results are compared to previous measurements from other groups using different methods, and general good agreement is found. However, we observe a significant discrepancy with some of the data from electron-beam-induced fluorescence that yield much larger cross sections for temperatures lower than 30 K.

An experimental setup for the production of pulsed supersonic He beams to be used for plasma edge diagnosis in fusion devices is described. A compromise between compact design, low cost, and good quality of the probe beams has been met. The main characteristics of the generated beams, such as pulse shape, absolute flux intensity, and velocity distribution, differ in general from those expected for ideal beam performance and have been determined and optimized experimentally. A first test of this He beam source at the TJ-I UP Torsatron in Madrid is also reported.

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