No abstract

Selective excitation of xenon by multiphoton absorption of a dye laser beam gives, in the VUV, the emissions characteristic of this gas, i.e., the resonance line at 147 nm, the first continuum at 150 nm and the second continuum at 173 nm. The kinetic analysis of these emissions was carried out, using a correlation method, between 10−2 and 600 Torr. At low pressures the temporal variation of the density of the resonant 3P1 states allowed the resonance line trapping phenomenon to be demonstrated and the natural lifetime of these states to be determined (τn =4.3 ns). At high pressures the metastable 3P2 states are involved in the emission of the second continuum. The excitation spectra plotted for the blue satellite showed the creation of states in the 4f configuration. This phenomenon indicates that multiphoton ionization is not responsible for the creation of the metastable states. These states are created from a crossing of two molecular levels, one of which is bound (0+u) and responsible for the first continuum and the other of which is dissociative (2u) and correlated to the 3P2 state.

The spectroscopic analysis of xenon at pressures between 50 and 700 torr shows the presence of several continuums over a wavelength range of 110–700 nm. The kinetics of two of them, 173 and 210 nm, are studied. In both cases, the shape of the light pulse, reconstituted by a time-amplitude conversion method, is defined by a difference of two exponential terms. These terms represent the formation and the decay of the molecular species. The variation of the time constants with pressure allows the reaction constants of the various processes in the kinetic scheme to be found. The continuum in the vuv is brought about by the 3Σ+u state formed by three-body collisions: k= (8.0±0.7)10−32 cm6 s−1 and the lifetime τ=102±2 ns; in the near uv, the molecular state has a shorter lifetime τ′1=8.2±0.5 ns but is formed like the previous one by three-body collisions: k3= (2.3±0.06)10−30 cm6 s−1. The near uv xenon emission constants ave very close to those we previously reported for argon and krypton.

M E T H O D SProduction of nodules and preparation of bacteroids. Nodules were produced on the roots of French-bean (Phaseolus uulgaris L. cv. Contander) inoculated with Rhizobium phaseoli strain 9-6, on soybean (Glycine max Merr. cv. Altona) inoculated with Rhizobium japonicum strain 1809, and on pea (Pisum satiuum L. cv. Centurion) inoculated with Rhizobium leguminosarum strain FH16. Plants were grown in a glasshouse as described previously .