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The Journal of Physical Chemistry A

Collisional Deactivation of Ba 5d7p 3D1 by Noble Gases

John E. Smedley, Sarah K. Coulter, Edward J. Felton, Kayla Zomlefer

Published Jul 17, 2008• 5 citations
Publisher

Abstract

Collisional deactivation of the 5d7p (3)D1 state of Ba by noble gases is studied by time- and wavelength-resolved fluorescence techniques. A pulsed, frequency-doubled dye laser at 273.9 nm excites the 5d7p (3)D1 level from the ground state, and fluorescence at 364.1 and 366.6 nm from the 5d7p (3)D1 --> 6s5d (3)D1 and 5d7p (3)D1 --> 6s5d (3)D2 transitions, respectively, is monitored in real time to obtain the deactivation rate constants. At 835 K these rate constants are as follows: He, (1.69 +/- 0.08) x 10(-9) cm(3) s(-1); Ne, (3.93 +/- 0.14) x 10(-10) cm(3) s(-1); Ar, (4.53 +/- 0.15) x 10(-10) cm(3) s(-1); Kr, (4.64 +/- 0.13) x 10(-10) cm(3) s(-1); Xe, (5.59 +/- 0.22) x 10(-10) cm(3) s(-1). From time-resolved 5d7p (3)D1 emission in the absence of noble gas and from the intercepts of the quenching plots, the lifetime of this state is determined to be 100 +/- 1 ns. Using time- and wavelength-resolved Ba emission with a low background pressure of noble gas, radiative lifetimes of several near-resonant states are determined from the exponential rise of the fluorescence signals. These results are as follows: 5d6d (3)D3, 28 +/- 3 ns; 5d7p (3)P1, 46 +/- 2 ns; 5d6d (3)G3, 21.5 +/- 0.8 ns; 5d7p (3)F3, 48 +/- 1 ns. Integrated fluorescence signals are used to infer the relative rate constants for population transfer from the 5d7p (3)D1 state to eleven near-resonant fine structure states.

DOI
10.1021/jp8022327

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Collisional deactivation of the 5d7p (3)D1 state of Ba by noble gases is studied by time- and wavelength-resolved fluorescence techniques. A pulsed, frequency-doubled dye laser at 273.9 nm excites the 5d7p (3)D1 level from the ground state, and fluorescence at 364.1 and 366.6 nm from the 5d7p (3)D1 --> 6s5d (3)D1 and 5d7p (3)D1 --> 6s5d (3)D2 transitions, respectively, is monitored in real time to obtain the deactivation rate constants. At 835 K these rate constants are as follows: He, (1.69 +/- 0.08) x 10(-9) cm(3) s(-1); Ne, (3.93 +/- 0.14) x 10(-10) cm(3) s(-1); Ar, (4.53 +/- 0.15) x 10(-10) cm(3) s(-1); Kr, (4.64 +/- 0.13) x 10(-10) cm(3) s(-1); Xe, (5.59 +/- 0.22) x 10(-10) cm(3) s(-1). From time-resolved 5d7p (3)D1 emission in the absence of noble gas and from the intercepts of the quenching plots, the lifetime of this state is determined to be 100 +/- 1 ns. Using time- and wavelength-resolved Ba emission with a low background pressure of noble gas, radiative lifetimes of several near-resonant states are determined from the exponential rise of the fluorescence signals. These results are as follows: 5d6d (3)D3, 28 +/- 3 ns; 5d7p (3)P1, 46 +/- 2 ns; 5d6d (3)G3, 21.5 +/- 0.8 ns; 5d7p (3)F3, 48 +/- 1 ns. Integrated fluorescence signals are used to infer the relative rate constants for population transfer from the 5d7p (3)D1 state to eleven near-resonant fine structure states.
Collisional excitation transfer and relaxation of K 5sp2\\sp2sp2P atoms in collisions with noble gases, as well as the radiative lifetimes of the K 5P, 6P and 7P fine-structure states have been investigated by methods of atomic fluorescence spectroscopy. Potassium vapour was mixed in a cell with a noble gas and selectively excited by pulsed dye-laser radiation to the 5sp2\\sp2sp2Psb1over2\\sb{1\\over2}sb1over2 or the 5sp2\\sp2sp2Psb3over2\\sb{3\\over 2}sb3over2 state in zero magnetic field and to the 5sp2\\sp2sp2Psb1over2−1over2\\sb{{1\\over 2}-{1\\over 2}}sb1over2−1over2 or the 5sp2\\sp2sp2Psb3over2−3over2\\sb{{3\\over 2}-{3\\over 2}}sb3over2−3over2 Zeeman substate in a field of 70 kG. Interferometric analysis of the fluorescence emitted from the directly (optically) excited state and that emitted from the collisionally populated states allowed the determination of the fine-structure mixing cross sections for collisions with He, Ne, Ar, Kr and Xe in zero magnetic field. Excitation transfer between Zeeman substates was investigated for collisions between the selectively excited 5P atoms and He, Ne and Ar atoms, allowing the determination of the multipole relaxation (depolarization) cross sections for dipole, quadrupole and octupole decay, as well as the Zeeman and fine-structure mixing cross sections and orientation transfer cross sections. A comparison of theoretical calculations with the experimental data has been made and the rate equations governing multipole relaxation and including effects due to strong fine-structure mixing on the multipole relaxation, have been described in detail. The radiative lifetimes of the individual fine-structure components of the K 5P, 6P and 7P states have been determined experimentally by means of time-resolved laser-induced fluorescence techniques. These data are compared with numerous theoretical calculations and the available experimental values.Dept. of Physics. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1988 .B474. Source: Dissertation Abstracts International, Volume: 49-04, Section: B, page: 1223. Thesis (Ph.D.)--University of Windsor (Canada), 1988.
We present a time resolved study of excitation transfer processes between the low lying excited states of barium (6s6p 3^{3}3PJ{\mathit{P}}_{\mathit{J}}PJ​, 6s5d 1^{1}1D2{\mathit{D}}_{2}D2​, 6s5d 3^{3}3DJ{\mathit{D}}_{\mathit{J}}DJ​) induced by collisions with noble gases. The transient excited state populations have been measured by means of fluorescence and absorption spectroscopy. Cross sections for spin-changing collisions from 3^{3}3P1{\mathit{P}}_{1}P1​ to 1^{1}1D2{\mathit{D}}_{2}D2​ and from 1^{1}1D2{\mathit{D}}_{2}D2​ to 3^{3}3D3{\mathit{D}}_{3}D3​ as well as for fine-structure mixing within the 3^{3}3D multiplet were obtained by fitting the numerical solution of a seven-state system of rate equations including diffusion to the experimental data. We compare our results to experimental findings for other alkaline earth metals and report an improved value of the lifetime of the 6s6p 3^{3}3P1{\mathit{P}}_{1}P1​ state of barium.
Electronically excited strontium atoms in the low-lying 5s5p(3PJ) state, 1.8 eV above the 5 s2(1S0) ground state, have been studied in the time-resolved mode by recording the forbidden emission at λ= 689.3 nm [Sr(53P1)→ Sr(51S0)+hν]. Sr(53P1) was generated by the repetitive pulsed dye-laser excitation of ground-state strontium atoms, in equilibrium with the solid at elevated temperatures, in a slow-flow system kinetically equivalent to a static system. The resulting resonance fluorescence at λ= 689.3 nm, following rapid Boltzmann equilibration within the 53PJ spin-orbit manifold, was then monitored by means of boxcar integration. Particular consideration was given to the development of a pre-trigger photomultiplier gating system which permitted decay measurements necessarily to be made on time scales considerably shorter than achieved hitherto with this type of investigation. Measurement of the fluorescence decays in the noble gases and across a range of atomic strontium concentration revealed significant effects due to radiation trapping. Extrapolation of the decay data to [Sr(51S0)]= 0 yielded the mean radiative lifetime τe= 20.1 ± 0.4 µs for the λ= 689.3 nm transition. This is compared with the range of values reported previously. The following upper limits are reported for the collisional-quenching constants of Sr(53PJ) by the noble gases (kQ/cm3 atom–1 s–1, T= 950 K): He, <5.5 × 10–15; Ne, <3.5 × 10–15; Ar, <3.9 × 10–15; Kr, <5.5 × 10–15 and Xe, <3.1 × 10–15, which are compared with data derived from the phase-shift technique. A limit is also reported of the rate constant for quenching of Sr(53PJ) by Sr(51S0) of <2 × 10–13 cm3 atom–1 s–1(T= 850–1000 K). The quenching of Sr(53PJ) by H2 and D2 is studied in detail, yielding the following results: kH2= 3.7 ± 0.4 × 10–12 cm3 molecule–1 s–1(950 K, 1 σ), kD2= 3.0 ± 0.2 × 10–12 cm3 molecule–1 s–1(950 K, 1 σ). The results for these two isotopes are compared with analogous data reported from other measurements for Ca(43PJ) and Mg(33PJ).
Time-resolved measurements of fluorescence and level populations have been made on barium vapour illuminated by an intense pulse of laser radiation (1 MW cm -2 , 50 ns FWHM) tuned to the resonance transition of Ba I, 6s 2 1 S 0 -6s6p 1 P 1 , at 5535 AA. Barium number densities between 10 13 -10 15 cm -3 were investigated, using a buffer gas of helium at 100 Torr. Fluorescence was measured with two different geometrical arrangements, one allowing partial spatial resolution. In neither case did the observed fluorescence saturate with increasing laser power, although the maximum flux was more than sufficient to burn through the vapour column, as confirmed by transmission measurements. The power loss from the laser beam was found to be compatible with the scattered radiation from the pumped column in the absence of radiation trapping. In contrast to other similar experiments, no significant ionisation was detected (<5%). Time-resolved population measurements by anomalous dispersion on the 6s6p 3 P 2 and 6s5d 1 D 2 metastable levels yielded quenching cross sections for both Ba-Ba and Ba-He collisions, but gave anomalous result for the peak populations. A qualitative explanation of the fluorescence anomaly is proposed on the basis of the AC Stark effect, and it is shown that the same effect can inhibit the onset of stimulated emission to the metastable D levels.
At different Rb densities,Rb vapor was irradiated in a glass fluorescence cell with pulses of radiation from a pumped-laser,populating Rb 2 (B 1 Π u)state by single-photon absorption.Energy transfer in Rb 2 (B 1 Π u) + Rb(5S) collision is studied using methods of atomic and molecular fluorescence.The decay signal of time-resolved fluorescence from B 1 Π u → X 1 Σ + g transition was monitored.The effective lifetimes of the B 1 Π u state can be resolved.The plot of reciprocal of effective lifetimes of the B 1 Π u state against Rb densities yielded the slope that indicated the total cross section for deactivation and the intercept that provided the radiative lifetime of the state.The radiative lifetime 23.5ns for the B 1 Π u is obtained.The cross section for deactivation of the Rb 2 (B 1 Π u) molecules by collisions with Rb atoms is σ 3=(4.33 ± 0.14) × 10-15 cm 2.At the different Rb densities,the time-integrated intensities of the resulting Rb emission lines.I(5P 3/2 → 5S 1/2) and I(5P 1/2 → 5S 1/2) were measured.The absolute values for Rb 2 (B 1 Π u)+Rb→ Rb 2 (1 1 Σ + g) + Rb(5P J)collisional transfer cross sections have been obtained.The cross sections are σ 31=(2.86 ± 0.13) × 10-16 cm 2 (for transferring to 5P 1/2) and σ 32=(8.30 ± 0.38) × 10-16 cm 2 (for transferring to 5P 3/2),respectively.