Inelastic Collisions between Excited Alkali Atoms and Molecules. VIII. 62P1/2–62P3/2 Mixing and Quenching in Mixtures of Rubidium with H2, HD, D2, N2, CH4, and CD4
Excitation transfer between the 62P fine-structure substates in rubidium, induced in inelastic collisions with ground-state molecules, has been studied using techniques of sensitized fluorescence. Rubidium vapor in mixtures with various molecular gases was irradiated with each component of the 2P rubidium doublet in turn, and measurements of sensitized-to-resonance fluorescent intensity ratios yielded the following mixing cross sections Q12(2P1/2 → 2P3/2) and Q21(2P1/2 ← 2P3/2), as well as effective quenching cross sections Q1X(2P1/2 → 2XJ″) and Q2X(2P3/2 → 2XJ″). For collisions with H2: Q12(2P1/2 → 2P3/2) = (41 ± 5) Å2; Q21(2P1/2 ← 2P3/2) = (26 ± 3) Å2; Q1X(2P1/2 → 2XJ″) = (36 ± 9) Å2; Q2X(2P3/2 → 2XJ″) = (31 ± 8) Å2. For HD: Q12 = (42 ± 5) Å2; Q21 = (27 ± 4) Å2; Q1X = (47 ± 13) Å2; Q2X = (38 ± 10) Å2. For D2: Q12 = (42 ± 5) Å2; Q21 = (27 ± 4) Å2; Q1X = (28 ± 8) Å2; Q2X = (21 ± 7) Å2. For N2: Q12 = (107 ± 15) Å2; Q21 = (70 ± 10) Å2; Q1X = (128 ± 44) Å2; Q2X = (126 ± 33) Å2. For CH4: Q12 = (38 ± 6) Å2; Q21 = (24 ± 3) Å2; Q1X = (129 ± 41) Å2; Q2X = (114 ± 37) Å2. For CD4: Q12 = (52 ± 7) Å2; Q21 = (34 ± 5) Å2; Q1X = (82 ± 30) Å2; Q2X = (76 ± 22) Å2. An analysis of these results suggests the possibility of resonances with various molecular rotational and vibrational transitions.
52P1/2 ↔ 52P3/2 mixing and 52S1/2 ← 52P1/2, 2P3/2 quenching in rubidium, induced in collisions with ground state H2, HD, D2, N2, CH4, CD4, C2H4, and C2H6 molecules, have been investigated using methods of sensitized fluorescence. The rubidium vapor mixed with each of the gases was excited in turn by each component of the rubidium resonance doublet, and the resulting fluorescence, emitted at right angles to the direction of the exciting light, was resolved into the two fine-structure components whose intensity ratios were measured in relation to the gas pressure using photon counting techniques. The measurements yielded the following cross sections for the mixing and quenching collisions.For H2: Q12(2P1/2 → 2P3/2) = 11 Å2, Q21(2P1/2 ← 2P3/2) = 15 Å2, Q10(2S1/2 ← 2P1/2) = 6 Å2, Q20(2S1/2 ← 2P3/2) = 3 Å2.[Formula: see text]The mixing cross sections agree with theoretical values within an order of magnitude.
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.
The cross sections for excitation transfer between the 62P fine-structure substates in rubidium, induced in collisions with noble gas atoms, have been determined in a series of sensitized fluorescence experiments. Mixtures of rubidium vapor and noble gases at pressures varying in the range 0–5 Torr were irradiated with each component of the second 2P rubidium doublet in turn and the following cross sections for 2P mixing were obtained from measurements of sensitised-to-resonance fluorescent intensity ratios. Rb–He: Q12(2P1/2 → 2P3/2) = 29.3 Å2; Q21(2P1/2 ← 2P3/2) = 19.0 Å2. Rb–Ne: Q12 = 10.3 Å2; Q21 = 6.4 Å2. Rb–Ar: Q12 = 24.0 Å2; Q21 = 14.9 Å2. Rb–Kr: Q12 = 23.2 Å2; Q21 = 14.6 Å2. Rb–Xe: Q12 = 43.9 Å2; Q21 = 27.7 Å2 In their dependence on the magnitude of the fine-structure splitting, the values are consistent with previously determined cross sections for mixing in the first and third 2P doublets of alkali atoms.
3 2P1/2 ↔ 3 2P3/2 excitation transfer in sodium, induced in inelastic collisions with ground-state N2, H2, HD, and D2 molecules, has been investigated in a series of sensitized fluorescence experiments. Mixtures of sodium vapor at a pressure of 5 × 10−7 Torr, and the gases, were irradiated with each NaD component in turn, and the fluorescence which contained both D components was monitored at right angles to the direction of the exciting beam. Measurements of the relative intensities of the NaD fluorescent components yielded the following collision cross sections for excitation transfer. For Na–N2 collisions: Q12(2P1/2 → P3/2) = 144 Å2, Q21(2P1,2 ← 2P3/2) = 76 Å2 for Na–H2 collisions: Q12 = 80 Å2, Q21 = 42 Å2. For Na–HD collisions: Q12 = 84 Å2, Q21 = 44 Å2. For Na–D2 collisions: Q12 = 98 Å2, Q21 = 52 Å2. The cross sections Q21 exhibit a slight resonance effect between the atomic and molecular rotational transitions.
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.
Excitation transfer between the 62P21 and 62P23 resonance states in cesium, induced by Cs-N2 and Cs-H2 collisions, was observed in the first experiment of its kind, in which techniques of sensitized fluorescence are used to investigate collisional mixing between resonance states of alkali atoms in mixtures with molecular gases. The cesium-vapor-gas system, in which the cesium vapor pressure was low enough to avoid radiation trapping, was irradiated with a single component of the resonance doublet. The fluorescent light, which contained both components of the doublet, was monitored at right angles to the direction of excitation. Measurements of relative intensities of the fluorescent components yielded the following cross sections for excitation transfer and for quenching of resonance radiation. For Cs-N2 collisions: ${Q}_{12}(^{2}P_{\frac{1}{2}}\ensuremath{\rightarrow}^{2}P_{\frac{3}{2}})=3.6$ A˚2, ${Q}_{21}(^{2}P_{\frac{1}{2}}\ensuremath{\leftarrow}^{2}P_{\frac{3}{2}})=16.2$ A˚2, ${Q}_{10}(^{2}S_{\frac{1}{2}}\ensuremath{\leftarrow}^{2}P_{\frac{1}{2}})=55.2$ A˚2, ${Q}_{20}(^{2}S_{\frac{1}{2}}\ensuremath{\leftarrow}^{2}P_{\frac{3}{2}})=63.5$ A˚2. For Cs-H2 collisions: Q12=6.7A˚2, Q21=29.6A˚2, Q10=11.7A˚2, Q20=6.7A˚2. The large sizes of the excitation-transfer cross sections, which are comparable to the corresponding Cs-Cs cross sections, are attributed to resonances with transitions in the molecules.