No abstract

Absolute rate constants for the ionization of highly excited xenon atoms in collisions with CH3I, C7F14, C6F6, and CH3Br have been measured and the major charged reaction products have been identified for all but CH3Br. Theoretical models view such collisions as being dominated by the interaction between the target molecules and the ’’essentially free’’ Rydberg electrons. It is thus predicted that the negative ions produced during collisional ionization are identical to those resulting from free electron attachment, and that the rate constants for collisional ionization are the same as those for free electron attachment. The present data are reviewed in light of these predictions.

Ionization of xenon atoms in single highly excited states ‖nf≳ (where 25⩽n⩽40) by collisions with CCl4, CCl3F, and SF6 has been investigated. Absolute rate constants for Xe+ production are reported together with the identities of the major negatively charged species produced in the collisions. Cross sections determined from these rate constants are also given. The data lend support to the theoretical model, which views such collisions as being dominated by the interaction between the target molecules and the excited electron, with the Xe+ ion core playing a minor role.

Effects due to the interaction of 300 K background radiation with Xe(nfj Rydberg atoms are reported. Transitions to nearby d and g levels are observed, When the ambient photon density is reduced to that appropriate to liquidnitrogen temperature by cooling the apparatus, a corresponding reduction in the transition rates to these levels is observed, The transition rates are found to be consistent with those predicted by use of quantum-defect theory.

Many spectroscopic studies require a source of coherent cw radiation tunable in the uv. Continuous wave radiation in the 257-360-nm range has been generated by sum frequency mixing, in potassium dihydrogen phosphate (KDP) and its isomorphs, selected output lines from an argon or krypton ion laser with the output of a cw dye laser. 1 Recent studies of mixing in potassium pentaborate (KB5) using pulsed laser systems 2 however suggested that cw radiation at wavelengths considerably shorter than 257 nm could be generated by mixing, in an angle-tuned KB5 crystal, with the uv output lines of an ion laser. The input wavelengths required to produce phase matched sum frequency mixing with the uv lines of an argon ion laser, calculated by use of the data obtained using pulsed laser systems, 2 are shown in Fig. 1, as a function of the angle between the direction of propagation of the interacting beams and the b axis of the crystal, for angle tuning in both the ab and bc planes. It is evident from Fig. 1 that, with input wavelengths readily available from cw dye laser systems, tunable uv radiation can be generated over a considerable wavelength range which extends below that obtainable by direct second harmonic generation. The present Letter reports the generation of tunable cw radiation in the 211-216-nm range by mixing in KB5.A Spectra-Physics model 375 dye laser was used in the present study and provided an output linewidth of ~0.5 Å. The dyes employed were rhodamine 110 and rhodamine 6G. The output of the dye laser was combined with the uv output of a Spectra-Physics model 171 argon ion laser by means of a dichroic mirror. The superposed beams, which were both vertically polarized, were optimally focused 3 into the mixing crystal by a 100-mm focal length fused quartz lens. In order to compensate for the chromatic aberration introduced by this lens, the dye laser beam was prefocused prior to superposition of the beams so that the interacting beams had common waists and focal positions within the crystal. The powers in the input beams were determined by use of a thermopile. The output beam emerging from the crystal was recollimated by a fused quartz lens and was separated from the remaining input radiation by a fused quartz prism. The output radiation was detected either by the fluorescence it generated on a phosphor screen or by a calibrated EMR type 541-G-08-18 solar blind photomultiplier, which was also used to determine the output power.The KB5 crystal employed was a cube of 10-mm sides with entrance and exit faces perpendicular to the b axis. The crystal was located in a sealed cell equipped with fused quartz windows and oriented such that the input beams were polarized along the α axis. The cell was fixed in a mount which provided rotation about a vertical axis. At other than normal incidence the two input beams are refracted through slightly different angles as they enter the mixing crystal, and, in con sequence, minor adjustments in input beam alignment are Fig. 1. Angle-tuning curves for sum frequency mixing with...