The Journal of Chemical Physics

Photoassociative spectroscopy of long-range states of ultracold 6Li2 and 7Li2

E. R. I. Abraham, Nicholas W. M. Ritchie, W. I. McAlexander, Randall G. Hulet

Published Nov 8, 1995• 91 citations

Abstract

We have obtained spectra of the high-lying vibrational levels of the A1Σu+ and 13Σg+states of both 6Li2 and 7Li2 via photoassociation of colliding ultracold atoms confined to a magneto-optical trap. Because of the low collision energies (∼1 mK), very high spectroscopic resolution is realized, and sensitivity is greatest for the usually difficult to access long-range states. Binding energies relative to the center of gravity of the resolved hyperfine structure are given for the A1Σu+ vibrational levels v =62–88 for 6Li2 and v=65–97 for 7Li2, and the 13Σg+ vibrational levels v=56–84 for 6Li2 and v=62–90 for 7Li2. These are extremely long-range levels with outer classical turning points ranging from 25 a0 to 220 a0, where a0 is the Bohr radius. The spectra arise mainly from s-wave collisions, and therefore exhibit little rotational structure.

DOI: 10.1063/1.470296

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The Journal of Chemical Physics

Photoassociative spectroscopy of long-range states of ultracold 6Li2 and 7Li2

E. R. I. Abraham, Nicholas W. M. Ritchie, W. I. McAlexander, Randall G. Hulet

Published Nov 8, 1995• 91 citations

Publisher

Abstract

DOI: 10.1063/1.470296

Related papers

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The spectra of the high-lying vibrational levels of the $A\\sp1\\Sigma\\sbsp{u}{+}$ and $1\\sp3\\Sigma\\sbsp{g}{+}$ singly excited states of both $\\sp6\\rm Li\\sb2$ and $\\sp7\\rm Li\\sb2$ are obtained via photoassociation of colliding ultracold atoms confined in a magneto-optical trap. The least bound state of the $a\\sp3\\Sigma\\sbsp{u}{+}$ ground state potential, obtained by two-photon photoassociative spectroscopy, is also presented for both $\\sp7\\rm Li\\sb2$ and $\\sp6\\rm Li\\sb2$ . The vibrational levels have resolved hyperfine structure, whose relative energy splittings and transition strengths are accurately modeled. The photoassociative spectra are used to precisely determine both the singlet and triplet s-wave scattering lengths for both isotopes, which are important parameters in systems designed to observe quantum degenerate effects and Bose-Einstein condensation.The spectra of the high-lying vibrational levels of the $A\\sp1\\Sigma\\sbsp{u}{+}$ and $1\\sp3\\Sigma\\sbsp{g}{+}$ singly excited states of both $\\sp6\\rm Li\\sb2$ and $\\sp7\\rm Li\\sb2$ are obtained via photoassociation of colliding ultracold atoms confined in a magneto-optical trap. The least bound state of the $a\\sp3\\Sigma\\sbsp{u}{+}$ ground state potential, obtained by two-photon photoassociative spectroscopy, is also presented for both $\\sp7\\rm Li\\sb2$ and $\\sp6\\rm Li\\sb2$. The vibrational levels have resolved hyperfine structure, whose relative energy splittings and transition strengths are accurately modeled. The photoassociative spectra are used to precisely determine both the singlet and triplet s-wave scattering lengths for both isotopes, which are important parameters in systems designed to observe quantum degenerate effects and Bose-Einstein condensation.

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We present spectra of hyperfine resolved vibrational levels of the ${\mathit{A}}^{1}$ ${\mathrm{\ensuremath{\Sigma}}}_{\mathit{u}}^{+}$and 1 ${\mathrm{}}^{3}$ ${\mathrm{\ensuremath{\Sigma}}}_{\mathit{g}}^{+}$ states of $^{6}\mathrm{Li}_{2}$ and $^{7}\mathrm{Li}_{2}$ obtained via photoassociation of colliding ultracold atoms in a magneto-optical trap. A simple first-order perturbation theory analysis accurately accounts for the frequency splittings and relative transition strengths of all observed hyperfine features. Assignment of the hyperfine structure allows accurate determination of a vibrational level center of gravity, which significantly decreases the experimental uncertainty of vibrational energies. Differences in the spectra of $^{6}\mathrm{Li}_{2}$ and $^{7}\mathrm{Li}_{2}$ are attributed to quantum statistics. The 1 ${\mathrm{}}^{3}$ ${\mathrm{\ensuremath{\Sigma}}}_{\mathit{g}}^{+}$ series obeys Hund's case ${\mathit{b}}_{\mathrm{\ensuremath{\beta}}\mathit{S}}$ coupling and the hyperfine constant is extracted for both isotopes. \textcopyright{} 1996 The American Physical Society.We present spectra of hyperfine resolved vibrational levels of the ${\mathit{A}}^{1}$${\mathrm{\ensuremath{\Sigma}}}_{\mathit{u}}^{+}$and 1${\mathrm{}}^{3}$${\mathrm{\ensuremath{\Sigma}}}_{\mathit{g}}^{+}$ states of $^{6}\mathrm{Li}_{2}$ and $^{7}\mathrm{Li}_{2}$ obtained via photoassociation of colliding ultracold atoms in a magneto-optical trap. A simple first-order perturbation theory analysis accurately accounts for the frequency splittings and relative transition strengths of all observed hyperfine features. Assignment of the hyperfine structure allows accurate determination of a vibrational level center of gravity, which significantly decreases the experimental uncertainty of vibrational energies. Differences in the spectra of $^{6}\mathrm{Li}_{2}$ and $^{7}\mathrm{Li}_{2}$ are attributed to quantum statistics. The 1${\mathrm{}}^{3}$${\mathrm{\ensuremath{\Sigma}}}_{\mathit{g}}^{+}$ series obeys Hund's case ${\mathit{b}}_{\mathrm{\ensuremath{\beta}}\mathit{S}}$ coupling and the hyperfine constant is extracted for both isotopes. \textcopyright{} 1996 The American Physical Society.

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The photoassociation of colliding ultracold trapped atoms permits the observation of high resolution molecular spectra of high lying vibrational levels with low total angular momentum and outer turning points greater than 50 Å. This paper describes how the hyperfine structure of alkali dimer molecules at large internuclear separation can be used to assign the electronic character of the observed photoassociation spectra and how hyperfine structure helps to explain the observed photoassociation spectrum of the attractive electronic states of the Na2 molecule that correlate with Na(3 2S)+Na(3 2P3/2) atoms.The photoassociation of colliding ultracold trapped atoms permits the observation of high resolution molecular spectra of high lying vibrational levels with low total angular momentum and outer turning points greater than 50 Å. This paper describes how the hyperfine structure of alkali dimer molecules at large internuclear separation can be used to assign the electronic character of the observed photoassociation spectra and how hyperfine structure helps to explain the observed photoassociation spectrum of the attractive electronic states of the Na2 molecule that correlate with Na(3 2S)+Na(3 2P3/2) atoms.

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The spectra of the high-lying vibrational levels of the

A\\sp1\\Sigma\\sbsp{u}{+}

and

1\\sp3\\Sigma\\sbsp{g}{+}

singly excited states of both

\\sp6\\rm Li\\sb2

and

\\sp7\\rm Li\\sb2

are obtained via photoassociation of colliding ultracold atoms confined in a magneto-optical trap. The least bound state of the

a\\sp3\\Sigma\\sbsp{u}{+}

ground state potential, obtained by two-photon photoassociative spectroscopy, is also presented for both

\\sp7\\rm Li\\sb2

and

\\sp6\\rm Li\\sb2

. The vibrational levels have resolved hyperfine structure, whose relative energy splittings and transition strengths are accurately modeled. The photoassociative spectra are used to precisely determine both the singlet and triplet s-wave scattering lengths for both isotopes, which are important parameters in systems designed to observe quantum degenerate effects and Bose-Einstein condensation.

We have obtained high-lying vibrational spectra for the

\\rm 1\\sp3\\Sigma\\sbsp{g}{+}

and

\\rm 1\\sp1\\Sigma\\sbsp{u}{+}

excited states of both

\\rm \\sp7Li\\sb2

and

\\rm \\sp6Li\\sb2

via photoassociation of colliding ultracold lithium atoms confined in a magneto-optical trap. Photoassociative spectroscopy of ultracold atoms is a powerful tool for probing molecular states near the dissociation energy that are inaccessible by other methods. For an ultracold lithium vapor, the distribution of unbound ground state energies is so small that precise free-bound spectroscopy is possible. Molecular hyperfine structure is resolved. We calculate accurate dissociation energies for both the

\\rm 1\\sp3\\Sigma\\sbsp{g}{+}

and

\\rm 1\\sp1\\Sigma\\sbsp{u}{+}

excited states of Li

\\sb2

. A model potential is constructed from a combination of experimental and theoretical information, and used to assign vibrational quantum numbers. We observe rotational structure and assign rotational quantum numbers.

We present spectra of hyperfine resolved vibrational levels of the

{\mathit{A}}^{1}

${\mathrm{\ensuremath{\Sigma}}}_{\mathit{u}}^{+}$and 1

{\mathrm{}}^{3}

${\mathrm{\ensuremath{\Sigma}}}_{\mathit{g}}^{+}$ states of

^{6}\mathrm{Li}_{2}

and

^{7}\mathrm{Li}_{2}

obtained via photoassociation of colliding ultracold atoms in a magneto-optical trap. A simple first-order perturbation theory analysis accurately accounts for the frequency splittings and relative transition strengths of all observed hyperfine features. Assignment of the hyperfine structure allows accurate determination of a vibrational level center of gravity, which significantly decreases the experimental uncertainty of vibrational energies. Differences in the spectra of

^{6}\mathrm{Li}_{2}

and

^{7}\mathrm{Li}_{2}

are attributed to quantum statistics. The 1

{\mathrm{}}^{3}

${\mathrm{\ensuremath{\Sigma}}}_{\mathit{g}}^{+}$ series obeys Hund's case ${\mathit{b}}_{\mathrm{\ensuremath{\beta}}\mathit{S}}$ coupling and the hyperfine constant is extracted for both isotopes. \textcopyright{} 1996 The American Physical Society.

300\\mu K (\\sim 7 MHz)

, so free-bound absorption lines are as sharp as bound-bound lines. Moreover, because of very long range centrifugal barriers, only a few collisional partial waves are important (

J^{\\prime\\prime} = 0, 1

and 2 in our work on

^{39}K

). Such photoassociative free-bound absorption allows observation of ``pure long-range molecule'' states (

R_{e} = 28

and 39 {\\AA} in

^{39}K_{2}

) as well as long-range levels of known short range states with outer classical turning points of

\\sim 20 - 250 {\\AA}

. Such spectra have been observed by ``trap loss'' (decrease in atomic fluorescence), molecular ionization, and fragment ionization. Optical-optical double resonance (OODR), e.g. through the ``Franck-Condon windows'' of the ``pure long-range'' states, produces readily assignable spectra at higher asymptotes as well. Further extensions of ultracold photoassociative spectroscopy and applications to determination of long range potentials, atomic properties, and Bose-Einstein condensate stability will be presented.