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Physical Review A

Experimental fine-structure branching ratios for Na–rare-gas optical collisions

Mark D. Havey, F. T. Delahanty, Linda L. Vahala, Gary E. Copeland

Published Oct 1, 1986• 21 citations
Publisher

Abstract

Experimental ratios for branching into the fine-structure levels of the Na 3p multiplet, as a consequence of an optical collision with He, Ne, Ar, Kr, or Xe, are reported. The process studied is Na(3s $^{2}S_{1/2}$)+scrR+nh\ensuremath{\nu}\ensuremath{\rightarrow} Na(3p $^{2}P_{j}$)+scrR+(n-1)h\ensuremath{\nu} , where scrR represents a rare-gas atom and where the laser frequency \ensuremath{\nu} is tuned in the wings of the Na resonance transitions. The branching ratios are defined as I(D1)/I(D2) where I(D1) and I(D2) are measured intensities of the atomic Na D1 and D2 lines. The ratios are determined for detunings ranging from about 650 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ in the blue wing to 170 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ in the red wing of the Na 3p multiplet. The branching is found to be strongly detuning dependent in the vicinity of the NaAr, NaKr, and NaXe near-red-wing satellites. The blue-wing branching ratios show a detuning-dependent approach to a recoil, or sudden statistical, limit of 0.5, irrespective of the rare gas. Fine-structure changing cross sections have also been measured for resonant excitation of the Na 3p $^{2}P_{j}$ state; the results are consistent with cross sections obtained from wing excitation.

DOI
10.1103/physreva.34.2758

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Physical Review A•Jul 1, 1994•9 citations
Experimental ratios for branching into the fine-structure levels of the Na 3p multiplet, as a consequence of an optical collision with He, Ne, Ar, Kr, or Xe, are reported. The process studied is Na(3s 2S1/2^{2}S_{1/2}2S1/2​)+scrR+nh\ensuremath{\nu}\ensuremath{\rightarrow} Na(3p 2Pj^{2}P_{j}2Pj​)+scrR+(n-1)h\ensuremath{\nu} , where scrR represents a rare-gas atom and where the laser frequency \ensuremath{\nu} is tuned in the wings of the Na resonance transitions. The branching ratios are defined as I(D1)/I(D2) where I(D1) and I(D2) are measured intensities of the atomic Na D1 and D2 lines. The ratios are determined for detunings ranging from about 650 cm\ensuremath−1{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}cm\ensuremath−1 in the blue wing to 170 cm\ensuremath−1{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}cm\ensuremath−1 in the red wing of the Na 3p multiplet. The branching is found to be strongly detuning dependent in the vicinity of the NaAr, NaKr, and NaXe near-red-wing satellites. The blue-wing branching ratios show a detuning-dependent approach to a recoil, or sudden statistical, limit of 0.5, irrespective of the rare gas. Fine-structure changing cross sections have also been measured for resonant excitation of the Na 3p 2Pj^{2}P_{j}2Pj​ state; the results are consistent with cross sections obtained from wing excitation.
Experimental ratios for branching into the fine‐structure levels of the Na 3p multiplet, as a consequence of an optical collision with He, Ne, Ar, Kr, or Xe, are reported. The process studied is Na(3s2S1/2) +RG+nhν → Na(3p2 Pj)+RG+(n−1)hν, where RG represents a rare gas atom and where the laser frequency ν is tuned in the wings of the Na resonance transitions. The branching ratios are defined as I(D1)/I(D2) where I(D1) and I(D2) are measured intensities of the atomic Na D1 and D2 lines. The ratios are determined for detunings ranging from about 650 cm−1 blue to 170 cm−1 red of the Na 3p multiplet. The branching is found to be strongly detuning dependent in the vicinity of the NaKr and NaXe near red‐wing satellites. The blue wing branching ratios show a detuning‐dependent approach to a recoil or sudden statistical limit of 0.5, irrespective of the rare gas.
Experimental ratios of branching in the fine-structure levels of the Rb5P multiplet, as a consequence of an optical collision with He, are reported. The process studied is Rb(5S1/2 )+ He + hrv --> Rb(5P(J)) +He, where the pulsed laser frequency v is tuned in the wings of the Rb resonance transitions. The authors defined the detuning delta to be v-v (D2 )(delta > 0) for laser frequency v highter than that of RbD2 transition and to be v-v (D1)(delta < 0) for v lower than the RbD1 transition. As RbHe molecular states are correlated to the two 5 2P(J) states, there is some likelihood that the molecule will dissociate into 5 2P1/2 or 5P3/2 state. The dissociation results in a nonuniform distribution of atomic Rb5P(J) states. The branching ratios are defined as n1/n2, where n1 and n2 are densities of the 5P1/2 and 5P3/2 states dissociated. To determine experimentally the relative cross section for scattering into the two fine-structure states, the relative time-intergrated intensities of the resulting Rb emission lines, I(5P3/2 --> 5P1/2 )[I(D2)] and I(5P1/2 --> 5P3/2) ) [I(D1)], were measured. The ratios are determined by detunings from about 200 cm(-1) in the blue wing to -180 cm(-1) in the red wing of the Rb5P multiplet. A rate equation analysis of the pressure dependence was yielded. The branching ratios and cross sections for collisional 5P1/2 --> 5P3/2 transition were obtained from the slope and intercept. The blue-wing branching ratios show a detuning-dependent approach to limit of 0. 2. The branching was found to be very large (-40) in the red wing, irrespective of the detuning. Fine structure changing cross section (1.1 +/- 0.3) x 10(-17) cm2 was measured from wing excitation, and the result is consistent with the cross section obtained from resonant excitation of the Rb5P(J) state. The measurements show a strong sensitivity to interatomic potentials and to nonadiabatic effects in dissociation dynamics.
Experimental ratio for branching into the fine structure levels of the Rb52P multiplet, as a consequence of an optical collision with Ar, is reported. An optically thin gaseous mixture of Rb and low-density Ar is excited by a cw dye laser. The excited RbAr molecule is dissociated into the Rb5P1/2 or Rb5P3/2, the branching ratio is defined as I(D1)/I(D2) where 1(D1) and I(D2) are measured intensities of the atomic RbD1 and D2 lines. The branching is determined for tuning ranging from 600 nm to 570 nm and in the Ar density range 2 to 8 X 1017 cm-3. The ratio of the dissociation rates and the fine structure changing cross section are obtained. The ratio of the dissociation rates approaches 0.7 as a limit which is independent of the laser frequency.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
The nonadiabatic close-coupled theory of atomic collisions in a radiation field is generalized to include electron spin and is used to consider the weak-field Na--rare-gas (RG) optical collision Na(2{(}^{2}(2S1/2{S}_{1/2}S1/2​)+RG+nh\ensuremath{\nu} \ensuremath{\mu}Na(2{(}^{2}(2Pj{\mathrm{P}}_{\mathrm{j}}Pj​)+RG+(n-1)h\ensuremath{\nu}. The effects of detuning and incident energy on the branching into the atomic Na 3p2{p}^{2}p2P3/2{P}_{3/2}P3/2​ and 3p 2P1/2^{2}P_{1/2}2P1/2​ states are examined. The cross sections \ensuremath{\sigma}(j) are found to have a strong asymmetry between red and blue detuning as well as a complex threshold and resonance structure dependence on energy. A partial cross-section analysis of \ensuremath{\sigma}(j) shows a significant difference between contributions from states of e and f molecular parity. The theoretically calculated detuning dependence of the branching ratio into each fine-structure state is in good agreement with available experimental data for Na-Ar, Na-Ne, and Na-He, as well as the total absorption coefficient for the production of Na 3p atoms. The fine-structure branching ratio for thermal energy collisions shows considerable variation with a rare-gas collision partner, due to the different interaction potentials. For sufficiently high collision energy, the branching approaches a recoil limit which is independent of collision partner.
Measurements of polarization of the Na 3p2{\mathit{p}}^{2}p2P3/2{\mathit{P}}_{3/2}P3/2​ level produced in Na-Ar, Na-Kr, and Na-Xe optical collisions are reported. The measurements extend over a range of detunings from 150 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ red to 350 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ blue of resonant excitation of the Na 3p levels. The short-pulse, pump-probe technique employed in the experiments eliminates large systematic effects due to the hyperfine interaction, collisions, and radiative trapping. For far-blue-wing excitation, nearly constant polarizations of 21(2)%, 13(2)%, and 8(2)% are obtained for Na-Ar, Na-Kr, and Na-Xe, respectively.
Experimental, polarization-dependent excitation spectra for excited-state-Mg--rare-gas-atom optical collisions are reported. In these first studies of the process, polarized Mg atoms in the 3p 1^{1}1P1{\mathit{P}}_{1}P1​ level are produced by absorption of linearly polarized light tuned to the 3s 1^{1}1S0{\mathit{S}}_{0}S0​\ensuremath{\rightarrow}3p 1^{1}1P1{\mathit{P}}_{1}P1​ resonance transition at 285.2 nm. Detuning-dependent, collision-induced polarization spectra are measured in a \ifmmode\pm\else\textpm\fi{}200-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ range around the Mg 3p 1^{1}1P1{\mathit{P}}_{1}P1​\ensuremath{\rightarrow}5s 1^{1}1S0{\mathit{S}}_{0}S0​ transition at 571.2 nm. The spectra correspond to probing transient Mg-Ne and Mg-Ar molecules on 3p $^{1}\mathrm{\ensuremath{\Pi}}_{1}$\ensuremath{\rightarrow}5s $^{1}\mathrm{\ensuremath{\Sigma}}_{0}^{+}$ and 3p $^{1}\mathrm{\ensuremath{\Sigma}}_{0}^{+}$\ensuremath{\rightarrow}5s $^{1}\mathrm{\ensuremath{\Sigma}}_{0}^{+}$ electronic transitions. Measurements of these excited-state polarization spectra for Mg-Ne optical collisions reveal that for detunings to the red of the atomic Mg 3p 1^{1}1P1{\mathit{P}}_{1}P1​\ensuremath{\rightarrow}5s 1^{1}1S0{\mathit{S}}_{0}S0​ transition, electronic linear polarization greater than 50% survives far into the molecular regime. This represents a direct measure of the polarization important to alignment-dependent inelastic processes in alkaline-earth-metal--rare-gas-atom collisions. The polarization spectra are discussed in terms of existing information on the interatomic potentials and through an axial recoil limit for the polarization degree for parallel and perpendicular molecular transitions. Rate coefficients k for disalignment of Mg 3p 1^{1}1P1{\mathit{P}}_{1}P1​ atoms by collisions with Ar [k=9.4(5)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ cm3{\mathrm{cm}}^{3}cm3/s] and with Ne [k=6.5(7)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ cm3{\mathrm{cm}}^{3}cm3/s] are also extracted from the data.