Sensitized Fluorescence in Vapors of Alkali Metals: Iv. Energy Transfer in Rubidium–rubidium Collisions

Sensitized fluorescence in rubidium vapor has been investigated in order to determine total cross sections for collisions of the second kind between rubidium atoms, leading to the transfer of excitation between the 5 2P1/2 and 5 2P3/2 resonance levels. The experiments were carried out at vapor pressures below 10−5 mm Hg, where there is virtually no imprisonment of resonance radiation. The exceedingly low fluorescent intensities were registered in an automatically programmed sequence of measurements, using photon counting techniques. The cross sections Q1(5 2P1/2 → 52P3/2) and Q2(5 2P1/2 ← 5 2P3/2) equal 53 Å2 and 68 Å2 respectively at 87 °C and 60 Å2 and 72 Å2 respectively at 107 °C. At both temperatures the ratios Q1/Q2 are in agreement with the values predicted by the principle of detailed balancing.