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Faraday Discussions of the Chemical Society

Preferential population of magnetic sublevels of photodissociated atoms. Photodissociation of alkali-metal dimers and the effect of magnetic field

Hajime Katô

Published Jan 1, 1986• 17 citations
Publisher

Abstract

By applying an external magnetic field, we have determined the population of the magnetic sublevels of photodissociated atoms from the intensities of atomic fluorescence lines split by the Zeeman effect. A preferential population of the magnetic sublevels of the atomic fragment Na(3 2P3/2), which arises from the direct photodissociation through the D1Π(continuum) state of the NaK molecule, has been observed. The results are explained by assuming the separability of electronic and nuclear motion during the dissociation. The observed results could be rationalized by the sum of the photodissociation amplitudes caused by excitation of the P, Q and R branches. The population of the magnetic sublevels of Rb(5 2P3/2) atoms produced by predissociation of the C1Πu state of the Rb2 molecule by the repulsive molecular state c3Σ+u has been determined from the Zeeman spectra of the emission Rb(5 2P3/2→ 5 2Sm′1/2). The observed results are interpreted by including the spin-orbit coupling between an excited level of the C1Πu state and levels of the c3Σ+u state and the effect of the external magnetic field.

DOI
10.1039/dc9868200001

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Preferential population of magnetic sublevels of photodissociated atoms. I. Predissociation of Cs2

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Preferential population of the magnetic sublevels of Cs(6p 2P3/2) atoms produced by predissociation of the C 1Πu state of the Cs2 molecule along the repulsive molecular state b 3Σ+u , has been found by observing the polarization of the atomic fluorescence Cs(6p 2Pm3/2→6s 2S1/2). By applying an external magnetic field, we have determined the population of the magnetic sublevels Cs(6p 2Pm3/2) directly from the intensities of the fluorescence lines Cs(6p 2Pm3/2 →6s 2Sm±11/2 ) split by the Zeeman effect. The results are analyzed theoretically by assuming the separability of electronic and nuclear motion for the dissociation along the repulsive potential curve. The effect of the external magnetic field on the photodissociation has been made clear, and the observed results could be fully explained on the basis of the adiabatic approximation.

The Journal of Chemical Physics•Feb 15, 1985•20 citations

Orientation observed by Zeeman spectra of dissociated atoms and the interference in photoexcitations

Yasuyuki Kimura, Shunji Kasahara, Hajime Katô +1 more

In a magnetic field, the wave number of a pump laser light polarized along the field was fixed to the isolated ${\mathrm{Cs}}_{2}D{}^{1}{\ensuremath{\Sigma}}_{u}^{+}(v=46,J=54)\ensuremath{\leftarrow}X{}^{1}{\ensuremath{\Sigma}}_{g}^{+}(v=0,J=55)$ line, and the excitation spectrum of the dissociated $\mathrm{Cs}(6p{}^{2}{P}_{3/2})$ atoms was measured by scanning the wave number of a probe laser light polarized perpendicular to the field. The population of each sublevel $6p{}^{2}{P}_{{3/2,m}_{j}}$ of the dissociated atoms was determined from the line intensities in the ${m}_{j}$-resolved excitation spectrum. The unequal population between the $6p{}^{2}{P}_{3/2,+|{m}_{j}|}$ and $6p{}^{2}{P}_{3/2,\ensuremath{-}|{m}_{j}|}$ levels (atomic orientation) was observed and it was enhanced as the magnetic-field strength was increased. The atomic orientation is shown to be induced by the interference between the indirect predissociation, which occurs by a combination of the spin-orbit coupling of the $D{}^{1}{\ensuremath{\Sigma}}_{u}^{+}$ state with the ${(2)}^{3}{\ensuremath{\Pi}}_{0u}$ state and the L-uncoupling and Zeeman interactions between the ${(2)}^{3}{\ensuremath{\Pi}}_{0u}$ and dissociative ${(2)}^{3}{\ensuremath{\Sigma}}_{u}^{+}$ states, and the dissociation following a direct excitation to the ${(2)}^{3}{\ensuremath{\Sigma}}_{u}^{+}$ state, which is allowed by spin-orbit coupling of the ${(2)}^{3}{\ensuremath{\Sigma}}_{u}^{+}$ state with the $B{}^{1}{\ensuremath{\Pi}}_{u}$ state. It is demonstrated that the atomic orientation is produced by the photodissociation in the presence of an external magnetic field even when all degenerated molecular $M=J,\dots{},0,\dots{},\ensuremath{-}J$ sublevels are excited by a light polarized linearly along the field.

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M j selectivity in collisional energy transfer between alkali-metal atoms

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Na atoms in the magnetic field have been selectively excited to each Zeeman sub-level of either the 3p2P1/2 or 3p 2P3/2 state by a tunable dye laser and the Zeeman spectra of the fluorescence from the collisional populated 3p 2P levels have been measured. From the intensities of the Zeeman lines, the selectivity in the collisional transitions between the Zeeman sub-levels of the 3p 2P1/2 and 3p 2P3/2 states has been directly specified. The time evolution of the σ-polarized fluorescence intensity of the Na(3p 2P1/2→ 3s 2S1/2) transition has been measured following the Na(3p 2P3/2â†� 3s 2S1/2) excitation by a σ-polarized short light pulse at H= 129 G. An amplitude modulation was found in the fluorescence from the collisional energy transferred state Na(3p 2P1/2). This is the first observation of quantum beats in collision-induced fluorescence. The frequency of the modulation coincides very well with that of the quantum beats of the resonance fluorescence Na(3p 2P3/2→ 3s 2S1/2), but the phases are opposite. These results are explained by assuming the conservation of coherence during collisional energy transfer.

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The theory of how excited-state hyperfine structure can be determined using a magnetic field to decouple the nuclear and electronic angular momentum is presented. The initial excited state is assumed to have an anisotropic Zeeman sublevel population distribution, which can be conveniently created by a laser-induced multiphoton excitation of an unpolarized atom. The Zeeman sublevel populations are subsequently mixed by the hyperfine interaction. The degree of mixing is controlled by a magnetic field applied along the quantization axis. The relative Zeeman sublevel populations can be monitored by detecting the polarization of fluorescence emitted when the excited state radiatively decays. It is convenient to take the ratio of two time-integrated fluorescent signals measured for orthogonal linear polarizations, since this is independent of the excited-state number density. The plot of this ratio versus magnetic field is very well approximated by a Lorentzian curve whose half-width is proportional to the magnetic dipole hyperfine coupling constant. This method was used to determine the magnitude of the magnetic dipole constant of the cesium 8${\mathit{D}}_{3/2}$ state to be 3.92\ifmmode\pm\else\textpm\fi{}0.10 MHz, which is in excellent agreement with previous results.

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Detection of NaRb Feshbach molecules by photodissociation

Fan Jia, Zhichao Guo, Lintao Li +1 more

We demonstrate detection of NaRb Feshbach molecules at high magnetic field by combining molecular photodissociation and absorption imaging of the photofragments. The photodissociation process is carried out via a spectroscopically selected hyperfine Zeeman level correlated with the Na ($3{P}_{3/2}$) $+$ Rb ($5{S}_{1/2}$) asymptote which, following spontaneous emission and optical pumping, leads to ground-state atoms in a single level with near unity probability. Subsequent to the dissociation, the number of molecules is obtained by detecting the resultant $^{23}\mathrm{Na}$ and $^{87}\mathrm{Rb}$ atoms. We have also studied the heating effect caused by the photodissociation process and optimized the detection protocol for extracting the temperature of the molecular cloud. This method enables the $in\phantom{\rule{0.16em}{0ex}}situ$ detection of fast timescale collision dynamics between NaRb Feshbach molecules and will be a valuable capability in studying few-body physics involving molecules.

arXiv:2010.04068•Physical Review A•Oct 28, 2020•7 citations

Hyperfine energy levels of alkali-metal dimers: Ground-state homonuclear molecules in magnetic fields

J. Aldegunde, Jeremy M. Hutson

We investigate the hyperfine energy levels and Zeeman splittings for homonuclear alkali-metal dimers in low-lying rotational and vibrational states, which are important for experiments designed to produce quantum gases of deeply bound molecules. We carry out density-functional theory calculations of the nuclear hyperfine coupling constants. For nonrotating states, the zero-field splittings are determined almost entirely by the scalar nuclear spin-spin coupling constant. By contrast with the heteronuclear case, the total nuclear spin remains a good quantum number in a magnetic field. We also investigate levels with rotational quantum number $N=1$, which have long-range anisotropic quadrupole-quadrupole interactions and may be collisionally stable. For these states the splitting is dominated by nuclear quadrupole coupling for most of the alkali-metal dimers and the Zeeman splittings are considerably more complicated.

arXiv:0810.4709•Physical Review A•Jan 6, 2009•40 citations
By applying an external magnetic field, we have determined the population of the magnetic sublevels of photodissociated atoms from the intensities of atomic fluorescence lines split by the Zeeman effect. A preferential population of the magnetic sublevels of the atomic fragment Na(3 2P3/2), which arises from the direct photodissociation through the D1Π(continuum) state of the NaK molecule, has been observed. The results are explained by assuming the separability of electronic and nuclear motion during the dissociation. The observed results could be rationalized by the sum of the photodissociation amplitudes caused by excitation of the P, Q and R branches. The population of the magnetic sublevels of Rb(5 2P3/2) atoms produced by predissociation of the C1Πu state of the Rb2 molecule by the repulsive molecular state c3Σ+u has been determined from the Zeeman spectra of the emission Rb(5 2P3/2→ 5 2Sm′1/2). The observed results are interpreted by including the spin-orbit coupling between an excited level of the C1Πu state and levels of the c3Σ+u state and the effect of the external magnetic field.
Preferential population of the magnetic sublevels of Cs(6p 2P3/2) atoms produced by predissociation of the C 1Πu state of the Cs2 molecule along the repulsive molecular state b 3Σ+u , has been found by observing the polarization of the atomic fluorescence Cs(6p 2Pm3/2→6s 2S1/2). By applying an external magnetic field, we have determined the population of the magnetic sublevels Cs(6p 2Pm3/2) directly from the intensities of the fluorescence lines Cs(6p 2Pm3/2 →6s 2Sm±11/2 ) split by the Zeeman effect. The results are analyzed theoretically by assuming the separability of electronic and nuclear motion for the dissociation along the repulsive potential curve. The effect of the external magnetic field on the photodissociation has been made clear, and the observed results could be fully explained on the basis of the adiabatic approximation.
In a magnetic field, the wave number of a pump laser light polarized along the field was fixed to the isolated ${\mathrm{Cs}}_{2}D{}^{1}{\ensuremath{\Sigma}}_{u}^{+}(v=46,J=54)\ensuremath{\leftarrow}X{}^{1}{\ensuremath{\Sigma}}_{g}^{+}(v=0,J=55)$ line, and the excitation spectrum of the dissociated Cs(6p2P3/2)\mathrm{Cs}(6p{}^{2}{P}_{3/2})Cs(6p2P3/2​) atoms was measured by scanning the wave number of a probe laser light polarized perpendicular to the field. The population of each sublevel 6p2P3/2,mj6p{}^{2}{P}_{{3/2,m}_{j}}6p2P3/2,mj​​ of the dissociated atoms was determined from the line intensities in the mj{m}_{j}mj​-resolved excitation spectrum. The unequal population between the 6p2P3/2,+∣mj∣6p{}^{2}{P}_{3/2,+|{m}_{j}|}6p2P3/2,+∣mj​∣​ and $6p{}^{2}{P}_{3/2,\ensuremath{-}|{m}_{j}|}$ levels (atomic orientation) was observed and it was enhanced as the magnetic-field strength was increased. The atomic orientation is shown to be induced by the interference between the indirect predissociation, which occurs by a combination of the spin-orbit coupling of the $D{}^{1}{\ensuremath{\Sigma}}_{u}^{+}$ state with the ${(2)}^{3}{\ensuremath{\Pi}}_{0u}$ state and the L-uncoupling and Zeeman interactions between the ${(2)}^{3}{\ensuremath{\Pi}}_{0u}$ and dissociative ${(2)}^{3}{\ensuremath{\Sigma}}_{u}^{+}$ states, and the dissociation following a direct excitation to the ${(2)}^{3}{\ensuremath{\Sigma}}_{u}^{+}$ state, which is allowed by spin-orbit coupling of the ${(2)}^{3}{\ensuremath{\Sigma}}_{u}^{+}$ state with the $B{}^{1}{\ensuremath{\Pi}}_{u}$ state. It is demonstrated that the atomic orientation is produced by the photodissociation in the presence of an external magnetic field even when all degenerated molecular $M=J,\dots{},0,\dots{},\ensuremath{-}J$ sublevels are excited by a light polarized linearly along the field.
Na atoms in the magnetic field have been selectively excited to each Zeeman sub-level of either the 3p2P1/2 or 3p 2P3/2 state by a tunable dye laser and the Zeeman spectra of the fluorescence from the collisional populated 3p 2P levels have been measured. From the intensities of the Zeeman lines, the selectivity in the collisional transitions between the Zeeman sub-levels of the 3p 2P1/2 and 3p 2P3/2 states has been directly specified. The time evolution of the σ-polarized fluorescence intensity of the Na(3p 2P1/2→ 3s 2S1/2) transition has been measured following the Na(3p 2P3/2â†� 3s 2S1/2) excitation by a σ-polarized short light pulse at H= 129 G. An amplitude modulation was found in the fluorescence from the collisional energy transferred state Na(3p 2P1/2). This is the first observation of quantum beats in collision-induced fluorescence. The frequency of the modulation coincides very well with that of the quantum beats of the resonance fluorescence Na(3p 2P3/2→ 3s 2S1/2), but the phases are opposite. These results are explained by assuming the conservation of coherence during collisional energy transfer.
The theory of how excited-state hyperfine structure can be determined using a magnetic field to decouple the nuclear and electronic angular momentum is presented. The initial excited state is assumed to have an anisotropic Zeeman sublevel population distribution, which can be conveniently created by a laser-induced multiphoton excitation of an unpolarized atom. The Zeeman sublevel populations are subsequently mixed by the hyperfine interaction. The degree of mixing is controlled by a magnetic field applied along the quantization axis. The relative Zeeman sublevel populations can be monitored by detecting the polarization of fluorescence emitted when the excited state radiatively decays. It is convenient to take the ratio of two time-integrated fluorescent signals measured for orthogonal linear polarizations, since this is independent of the excited-state number density. The plot of this ratio versus magnetic field is very well approximated by a Lorentzian curve whose half-width is proportional to the magnetic dipole hyperfine coupling constant. This method was used to determine the magnitude of the magnetic dipole constant of the cesium 8D3/2{\mathit{D}}_{3/2}D3/2​ state to be 3.92\ifmmode\pm\else\textpm\fi{}0.10 MHz, which is in excellent agreement with previous results.
We demonstrate detection of NaRb Feshbach molecules at high magnetic field by combining molecular photodissociation and absorption imaging of the photofragments. The photodissociation process is carried out via a spectroscopically selected hyperfine Zeeman level correlated with the Na (3P3/23{P}_{3/2}3P3/2​) +++ Rb (5S1/25{S}_{1/2}5S1/2​) asymptote which, following spontaneous emission and optical pumping, leads to ground-state atoms in a single level with near unity probability. Subsequent to the dissociation, the number of molecules is obtained by detecting the resultant 23Na^{23}\mathrm{Na}23Na and 87Rb^{87}\mathrm{Rb}87Rb atoms. We have also studied the heating effect caused by the photodissociation process and optimized the detection protocol for extracting the temperature of the molecular cloud. This method enables the insituin\phantom{\rule{0.16em}{0ex}}situinsitu detection of fast timescale collision dynamics between NaRb Feshbach molecules and will be a valuable capability in studying few-body physics involving molecules.
We investigate the hyperfine energy levels and Zeeman splittings for homonuclear alkali-metal dimers in low-lying rotational and vibrational states, which are important for experiments designed to produce quantum gases of deeply bound molecules. We carry out density-functional theory calculations of the nuclear hyperfine coupling constants. For nonrotating states, the zero-field splittings are determined almost entirely by the scalar nuclear spin-spin coupling constant. By contrast with the heteronuclear case, the total nuclear spin remains a good quantum number in a magnetic field. We also investigate levels with rotational quantum number N=1N=1N=1, which have long-range anisotropic quadrupole-quadrupole interactions and may be collisionally stable. For these states the splitting is dominated by nuclear quadrupole coupling for most of the alkali-metal dimers and the Zeeman splittings are considerably more complicated.