Measurement of cross-sections for transfer of excitation : sensitized fluorescence in caesium vapour

D. A. McGillis

Collisions of the second kind between caesium and caesium, caesium and helium, and caesium and xenon atoms, leading to P p the transfer of excitation between the 6 6 P^yg states in caesium, have been investigated by studying the sensitized fluorescence in caesium vapor at pressures in the range 2x10*^ • 7x10*5 mm Hg and in vapor-inert gas mixtures.These low caesium densities, at which trapping of resonance radiation is virtually absent, were previously Inaccesible to such measurements.The use of a high intensity light source and an improved fluorescence cell in conjunction with a very sensitive detection system, permitted accurate measurements of extremely low fluorescent intensities.The total collision cross sections for the processes ô^P^yg -> and 6 %]^yg<r-G^P^yg equal 0.64x10*^^ cm® and 3.1x10*15 ^^2 for caesium-caesium collisions, 0.41x10*®® cm® and 2.7x10*®® cm® for caesium-helium collisions, and 7 .6x10 *®! cm^ and 2.9x10*1^ cm® for caesium-xenon collisions respectively.The ratios of these cross sections agree well with the values predicted by the principle of detailed balancing except for the caesiumxenon collisions, where a shielding effect has been postulated to account for the discrepancy.ill

Michel Pimbert, J. Cuvellier, J. Pascale +1 more

A. Czajkowski, M. Czajkowski

Collisional transfer of excitation energy from cadmium to caesium was investigated using methods of sensitized fluorescence. A mixture of cadmium and caesium vapors at low pressure was irradiated with Cd 3263.0 Å resonance radiation producing a population of Cd (53P1) atoms whose inelastic collisions with ground-state Cs atoms resulted in a transfer of excitation energy to a close-lying S, P, D and F states in caesium. The subsequent decay of these states manifested itself in the emission of sensitized fluorescence spectrum. Intensity measurements on the components of the spectrum by means of energy calibrated detector yielded some 50 cross-section values whose magnitudes range from 0.2 Å2 to 30.0 Å2 and which exhibit a pronounced resonances with ΔE the energy defect between Cd (53P1) and the appropriate level in caesium.

K. T. Hecht

M. Stupavsky

P^2P3/2 m ^-x^n8 *n sodium vapour, induced by inelastic collisions with the diatomic molecules HD, and N^, was studied using techniques of sensitized fluorescence.The mixtures of sodium vapour with the various molecular gases were irradiated with one component of the appropriate resonance doublet.The fluorescence which contained both components of the doublet, was monitored at right angles to the direction of excitation.The measurement of the relative intensities of the fluorescent components 2 yielded the total inelastic cross sections for P mixing, Ql2(2Pi/2---> 2p3/2^ and ^21^2pi/2^---' 2p3/2^* The sodium vaPour *n 5. Cross Sections for 3 P. ---3 P. Mixing Induced by Sodium Molecule Collisions.38 6. Cross Sections for Excitation Transfer in Na-Molecule Collisions, together with the Corresponding Relative Velocity of the Colliding Partners 42 2 2 7. Comparison of the Cross Sections for P. ---^-s/o Mixing Induced by Alkali Atom-Molecule Collisions 43 vi