The effects of imprisonment of resonance radiation in potassium vapor and of collisions between excited potassium atoms and N2, H2, HD, and D2 molecules, on the measured lifetimes of the 42P states, have been investigated by the method of delayed coincidences. The potassium atoms were excited with short pulses of resonance radiation, and the delays between the exciting and fluorescent pulses were measured with a time-to-amplitude converter. At pure potassium densities below 1010 atoms/cm3, the measured lifetimes approach the constant values 27.8 ± 0.8 and 27.6 ± 0.8 ns, corresponding to the natural lifetimes of the 42P1/2 and 42P3/2 states, respectively. At higher densities the effective lifetimes are in satisfactory agreement with the predictions of Holstein's theory. The decrease in the measured decay rates observed upon addition of the diatomic gases yielded cross sections for quenching collisions with N2, H2, HD, and D2 which equal 34.0 ± 2.0 Å2, 9.4 ± 1.3 Å2, 11.9 ± 1.5 Å2, and 8.0 ± 2.0 Å2, respectively.
The effects of imprisonment of resonance radiation in potassium vapor and of collisions between excited potassium atoms and N2, H2, HD, and D2 molecules, on the measured lifetimes of the 42P states, have been investigated by the method of delayed coincidences. The potassium atoms were excited with short pulses of resonance radiation, and the delays between the exciting and fluorescent pulses were measured with a time-to-amplitude converter. At pure potassium densities below 1010 atoms/cm3, the measured lifetimes approach the constant values 27.8 ± 0.8 and 27.6 ± 0.8 ns, corresponding to the natural lifetimes of the 42P1/2 and 42P3/2 states, respectively. At higher densities the effective lifetimes are in satisfactory agreement with the predictions of Holstein's theory. The decrease in the measured decay rates observed upon addition of the diatomic gases yielded cross sections for quenching collisions with N2, H2, HD, and D2 which equal 34.0 ± 2.0 Å2, 9.4 ± 1.3 Å2, 11.9 ± 1.5 Å2, and 8.0 ± 2.0 Å2, respectively.
The met h o d of delayed coincidences for measu r i n g lifetimes of excited states has been used to investigate imprisonment of radiation in potassium vapor and to measure quenching cross sections in mixtures of potassium w ith diatomic gases and sodium wi t h noble gases.The me thod has also been u s e d to investigate the possibility that a longlived molec u l a r complex might be formed in inelastic collisions between 2 potassium and xenon, which lead to excitation transfer between the P potassium states.The alkali metal atoms were excited w i t h short pulses of resonance radiation, and the delays between the exciting and fluores cent pulses were m e a s u r e d w i t h a time-to-amplitude converter.At 10 3 pure potassium densities below 10 atoms/cm , the m e a s u r e d lifetimes approach the constant values of 27.8 + 0 .8 and 27.6 + 0 .8 nsec, 2 2 corresponding to the m e a n lifetimes of the 4 ^^2 anc* ^ ^3 / 2 s t a t e s > respectively.At higher densities, the apparent lifetimes are in satisfactory agreement w i t h the predictions of H o l s t e i n 's theory.The decrease in the apparent lifetimes, u p o n addition of diatomic gases to the potassium vapor, yielded cross sections for quenching collisions w it h N^, H^, HD and D^, which equal 34.0 + 2 .0 X2, 9.4 + 1.3 X2, 11.9 + 1.5 X2 and 8 .0 + 2 .0 X2, respectively.Addition of the noble gases He, Ne, Kr, Ar and Xe to sodium vapor did not lead to any measurable change in the decay rates for the sodium states within the iii
The cross sections for quenching collisions between excited sodium atoms and N2, H2, HD, and D2 molecules in their electronic ground states have been determined using a delayed-coincidence method. The sodium atoms in mixtures with the gases were excited with 20-nsec pulses of NaD radiation, and the delays between the exciting and fluorescent pulses were measured with a time-to-pulse-height converter. The resulting pulse-height spectra, which were accummulated in a 400-channel kicksorter, yielded the effective lifetimes ${\ensuremath{\tau}}^{\ensuremath{'}}$ of the sodium resonance state, which are shorter than the natural lifetime $\ensuremath{\tau}$ because of the nonradiative decay induced in collisions with the molecules. The cross sections for collisions with N2, H2, HD, and D2, obtained from an analysis of the dependence of ${\ensuremath{\tau}}^{\ensuremath{'}}$ on the gas pressures, are 30.4\ifmmode\pm\else\textpm\fi{}1.2, 16.2\ifmmode\pm\else\textpm\fi{}0.3, 11.6\ifmmode\pm\else\textpm\fi{}0.4, and 9.8\ifmmode\pm\else\textpm\fi{}0.3 A˚2, respectively.
4 2P1/2–4 2P3/2 mixing in potassium, induced by collisions with N2, H2, D2, and HD, was studied using techniques of sensitized fluorescence. The potassium vapor-gas systems, in which the potassium vapor pressure was kept very low to avoid radiation trapping, was irradiated with one component of the resonance doublet. The fluorescence which contained both components of the doublet was monitored at right angles to the direction of excitation. The following cross sections for mixing and quenching were obtained from measurements of relative intensities of the fluorescent components. For K–N2 collisions: Q12(2P1/2 → 2P3/2) = 100 Å2, Q21(2P1/2 ← 2P3/2) = 66 Å2, Q10(2S1/2 ← 2P1/2) = 35 Å2, Q20(2S1/2 ←2P3/2) = 39 Å2. For K–H2 collisions: Q12 = 76 Å2, Q21 = 53 Å2, Q10 = 7 Å2, Q20 = 4 Å2. For K–D2: Q12 = 72 Å2, Q21 = 50 Å2, Q10 = 2 Å2, Q20 = 1 Å2. For K–HD: Q12 = 74 Å2, Q21 = 49 Å2, Q20 = 11 Å2, Q20 = 14 Å2. An analysis of these results suggests the presence of resonances with the molecular rotational levels.
The total cross sections for collisions between excited potassium and unexcited rubidium atoms, leading to the transfer of excitation between the 42P states in potassium, have been determined in a sensitized fluorescence experiment. The experiments were carried out at partial pressures of potassium vapor lower than 10−5 mm Hg, at which the imprisonment of resonance radiation may be disregarded. The cross sections Q12″ (42P1/2 → 42P3/2) and Q21″ (42P1/2 ← 42P3/2) equal 260 Å2 and 175 Å2, respectively, and are in the ratio predicted by the principle of detailed balancing.
The effect of imprisonment of radiation in sodium vapor on the measured lifetime of the 32P states has been investigated in an experiment in which the atoms in the vapor were excited with 10-nsec pulses of resonance radiation and the elapsed times between the exciting and the fluorescent pulses were recorded using a time-to-amplitude converter and kicksorter. At vapor densities below 1010 atoms/cm3, where there is no multiple scattering, the measured lifetime reaches a constant value of (1.63\ifmmode\pm\else\textpm\fi{}0.04)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ sec, equal to the natural lifetime of the 32P states. In the density range 109-1013 atoms/cm3, the variation of the effective lifetime with the vapor density is in good agreement with the predictions of Milne's theory of radiation trapping; agreement with Holstein's theory is observed only in the range 1012-1013 atoms/cm3. The results of a subsidiary Hanle experiment show that a multiply scattered photon of sodium resonance fluorescence loses its original polarization and that, at high sodium vapor pressure, coherence is not preserved.
6 2P1/2 ↔ 6 2P3/2 mixing and 6 2S1/2 ← 6 2P1/2,3/2 quenching in cesium, induced in collisions with ground state N2, H2, HD, and D2 molecules, have been investigated using techniques of sensitized fluorescence. Mixtures of cesium vapor and the gases, in which the cesium vapor pressure was kept very low to avoid multiple scattering, were irradiated with each component of the cesium resonance doublet in turn. The fluorescence which contained both components of the doublet was observed in a direction perpendicular to that of the exciting beam. Measurements of the relative intensities of the fluorescent components yielded the following cross sections for mixing and quenching. For Cs–N2 collisions: Q12(2P1/2 → 2P3/2) = 4.7 Å2, Q21(2P1/2 ← 2P3/2) = 25 Å2, Q10(2S1/2 ← 2P1/2) = 77 Å2, Q20(2S1/2 ← 2P3/2) = 69 Å2. For Cs–H2 collisions: Q12 = 6.7 Å2, Q21 = 44 Å2, Q10 = 7 Å2, Q20 = 5 Å2. For Cs–HD collisions: Q12 = 4.8 Å2, Q21 = 32 Å2, Q10 = 4 Å2, Q20 = 3 Å2. For Cs–D2 collisions: Q12 = 4.2 Å2, Q21 = 28 Å2, Q10 = 8 Å2, Q20 = 7 Å2. The Cs–N2 and Cs–H2 cross sections supersede the values published previously (McGillis and Krause 1967). The cross sections Q21 appear to exhibit resonances with molecular rotational transitions.