Physical Review A

Hyperfine and vibrational structure of weakly bound levels of the lowest 1g state of molecular 87 Rb 2

Chin‐Chun Tsai, T. H. Bergeman, Eite Tiesinga, Paul S. Julienne, Daniel J. Heinzen

Published Nov 13, 2013• 4 citations

Abstract

Photoassociation resonances in the ${}^{87}$Rb${}_{2}$ ${1}_{g}$ state dissociating to $5{\phantom{\rule{0.16em}{0ex}}}^{2}S+5{}^{2}{P}_{1/2}$ were produced by the excitation of colliding ${}^{87}$Rb atoms in a far-off resonance trap. Levels down to 31 cm${}^{\ensuremath{-}1}$ below the dissociation limit were measured with resonance linewidths of 15 to 20 MHz, and have been located to a one-sigma combined systematic and statistical uncertainty of 50 MHz relative to the $5{\phantom{\rule{0.16em}{0ex}}}^{2}S+5{}^{2}{P}_{1/2}$ limit. Electron and nuclear spins were fixed to a space-fixed axis by circularly polarized optical pumping, so that only states with total nuclear spin $I=3$ were excited, thereby greatly simplifying the spectrum. The analysis of the data yielded hyperfine coupling parameters $A(v)$, vibrational $G(v)$, and rotational $B(v)$ parameters. The $G(v)$ parameters could be fit to an rms accuracy of about 0.01 cm${}^{\ensuremath{-}1}$ to a potential constructed from current ${C}_{3}$ and ${C}_{6}$ long-range dispersion parameters plus an ab initio potential that was adjusted in depth and with quadratic terms in the internuclear distance added to the inner wall.

DOI: 10.1103/physreva.88.052509

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Level structure of deeply bound levels of the c3Σg+ state of Rb287

Björn Drews, Markus Deiß, Joschka Wolf +2 more

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Observation of hyperfine interaction in photoassociation spectra of ultracold RbYb

Cristian Bruni, Axel Görlitz

Physical Review AAug 3, 201615 citations

Near-threshold photoassociation of 87Rb2

M. Kemmann, Ivan Mistrík, S. Nußmann +3 more

Physical Review AFeb 26, 200437 citations

Weakly bound 87 Rb 2 (5s1/2+5p1/2)1g molecules: Hyperfine interaction and LeRoy-Bernstein analysis including linear and nonlinear terms

Haikel Jelassi, Laurence Pruvost

Physical Review AMar 20, 201410 citations

PHOTOASSOCIATION SPECTROSCOPY OF ${^{85}}Rb_{2}$ NEAR ITS DISSOCIATION LIMIT

R. S. Freeland, Ph. W. Courteille, Chin‐Chun Tsai +4 more

Jan 1, 19980 citations

Photoassociation of85Rb atoms into 0u+states near the 5S+5P atomic limits

T. H. Bergeman, J Qi, Dajun Wang +8 more

New photoassociation data on the 0u+ levels of Rb2 below the 5S+5P1/2 limit are combined with older data (Cline et al 1994 Phys. Rev. Lett. 73 632) in a fit to potentials and spin–orbit functions. The P1/2 data exhibit oscillations in the B(v) values due to coupling between the two 0u+ series, as modelled accurately by a coupled potentials approach. The fitted value for the C3 dispersion parameter from the combined data agrees well with the value derived from the pure long-range 0g− state.

Journal of Physics B Atomic Molecular and Optical PhysicsSep 25, 200653 citations

Physical Review A

Hyperfine and vibrational structure of weakly bound levels of the lowest 1g state of molecular 87 Rb 2

Chin‐Chun Tsai, T. H. Bergeman, Eite Tiesinga, Paul S. Julienne, Daniel J. Heinzen

Published Nov 13, 2013• 4 citations

Publisher

Abstract

Photoassociation resonances in the

{}^{87}

{}_{2}

{1}_{g}

state dissociating to

5{\phantom{\rule{0.16em}{0ex}}}^{2}S+5{}^{2}{P}_{1/2}

were produced by the excitation of colliding

{}^{87}

Rb atoms in a far-off resonance trap. Levels down to 31 cm

{}^{\ensuremath{-}1}

below the dissociation limit were measured with resonance linewidths of 15 to 20 MHz, and have been located to a one-sigma combined systematic and statistical uncertainty of 50 MHz relative to the

5{\phantom{\rule{0.16em}{0ex}}}^{2}S+5{}^{2}{P}_{1/2}

limit. Electron and nuclear spins were fixed to a space-fixed axis by circularly polarized optical pumping, so that only states with total nuclear spin

I=3

were excited, thereby greatly simplifying the spectrum. The analysis of the data yielded hyperfine coupling parameters

A(v)

, vibrational

G(v)

, and rotational

B(v)

parameters. The

G(v)

parameters could be fit to an rms accuracy of about 0.01 cm

{}^{\ensuremath{-}1}

to a potential constructed from current

{C}_{3}

and

{C}_{6}

long-range dispersion parameters plus an ab initio potential that was adjusted in depth and with quadratic terms in the internuclear distance added to the inner wall.

DOI: 10.1103/physreva.88.052509

Related papers

Level structure of deeply bound levels of the c3Σg+ state of Rb287

Björn Drews, Markus Deiß, Joschka Wolf +2 more

We spectroscopically investigate the hyperfine, rotational, and Zeeman structure of the vibrational levels ${v}^{\ensuremath{'}}=0,7,13$ within the electronically excited $c{\phantom{\rule{0.222222em}{0ex}}}^{3}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}$ state of $^{87}\mathrm{Rb}_{2}$ for magnetic fields of up to $1000\phantom{\rule{0.28em}{0ex}}\text{G}$ . As spectroscopic methods we use short-range photoassociation of ultracold Rb atoms as well as photoexcitation of ultracold molecules which have been previously prepared in several well-defined quantum states of the $a{\phantom{\rule{0.222222em}{0ex}}}^{3}\mathrm{\ensuremath{\Sigma}}{}_{u}^{+}$ potential. As a by-product, we present optical two-photon transfer of weakly bound Feshbach molecules into $a{\phantom{\rule{0.222222em}{0ex}}}^{3}\mathrm{\ensuremath{\Sigma}}{}_{u}^{+}$, $v=0$ levels featuring different nuclear spin quantum numbers. A simple model reproduces well the molecular level structures of the $c{\phantom{\rule{0.222222em}{0ex}}}^{3}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}$ vibrational states and provides a consistent assignment of the measured resonance lines. Furthermore, the model can be used to predict the relative transition strengths of the lines. From fits to the data we extract for each vibrational level the rotational constant, the effective spin-spin interaction constant, as well as the Fermi contact parameter and the anisotropic hyperfine constant. In an alternative approach, we perform coupled-channel calculations where we fit the relevant potential energy curves, spin-orbit interactions, and hyperfine functions. The calculations reproduce the measured hyperfine level term frequencies with an average uncertainty of $\ifmmode\pm\else\textpm\fi{}9\phantom{\rule{0.28em}{0ex}}\mathrm{MHz}$, similar as for the simple model. From these fits we obtain a section of the potential energy curve for the $c{\phantom{\rule{0.222222em}{0ex}}}^{3}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}$ state which can be used for predicting the level structure for the vibrational manifold ${v}^{\ensuremath{'}}=0$ to 13 of this electronic state.We spectroscopically investigate the hyperfine, rotational, and Zeeman structure of the vibrational levels ${v}^{\ensuremath{'}}=0,7,13$ within the electronically excited $c{\phantom{\rule{0.222222em}{0ex}}}^{3}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}$ state of $^{87}\mathrm{Rb}_{2}$ for magnetic fields of up to $1000\phantom{\rule{0.28em}{0ex}}\text{G}$. As spectroscopic methods we use short-range photoassociation of ultracold Rb atoms as well as photoexcitation of ultracold molecules which have been previously prepared in several well-defined quantum states of the $a{\phantom{\rule{0.222222em}{0ex}}}^{3}\mathrm{\ensuremath{\Sigma}}{}_{u}^{+}$ potential. As a by-product, we present optical two-photon transfer of weakly bound Feshbach molecules into $a{\phantom{\rule{0.222222em}{0ex}}}^{3}\mathrm{\ensuremath{\Sigma}}{}_{u}^{+}$, $v=0$ levels featuring different nuclear spin quantum numbers. A simple model reproduces well the molecular level structures of the $c{\phantom{\rule{0.222222em}{0ex}}}^{3}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}$ vibrational states and provides a consistent assignment of the measured resonance lines. Furthermore, the model can be used to predict the relative transition strengths of the lines. From fits to the data we extract for each vibrational level the rotational constant, the effective spin-spin interaction constant, as well as the Fermi contact parameter and the anisotropic hyperfine constant. In an alternative approach, we perform coupled-channel calculations where we fit the relevant potential energy curves, spin-orbit interactions, and hyperfine functions. The calculations reproduce the measured hyperfine level term frequencies with an average uncertainty of $\ifmmode\pm\else\textpm\fi{}9\phantom{\rule{0.28em}{0ex}}\mathrm{MHz}$, similar as for the simple model. From these fits we obtain a section of the potential energy curve for the $c{\phantom{\rule{0.222222em}{0ex}}}^{3}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}$ state which can be used for predicting the level structure for the vibrational manifold ${v}^{\ensuremath{'}}=0$ to 13 of this electronic state.

arXiv:1703.07752Physical Review AJun 23, 20175 citations

Observation of hyperfine interaction in photoassociation spectra of ultracold RbYb

Cristian Bruni, Axel Görlitz

We report on the creation of ultracold heteronuclear and electronically excited Rb*Yb molecules in a hybrid conservative trap by photoassociation of ultracold $^{87}\mathrm{Rb}$ and $^{176}\mathrm{Yb}$ . The molecules are formed below the ${\mathrm{Rb}}_{5\mathit{p}1}(^{2}P_{1/2})+{\mathrm{Yb}}_{6\mathit{s}2}(^{1}S_{0})$ dissociation limit and the resonances are detected using trap-loss spectroscopy. By addressing vibrational levels with binding energies down to ${E}_{B}=\ensuremath{-}h\ifmmode\times\else\texttimes\fi{}2.2\phantom{\rule{0.16em}{0ex}}\mathrm{THz}$, we study the change in hyperfine coupling of the diatomic molecule as a function of internuclear separation. We observe a decreasing hyperfine splitting for more tightly bound excited molecular states where the hyperfine splitting is reduced by more than $30%$ compared to the atomic value for $^{87}\mathrm{Rb}$ .We report on the creation of ultracold heteronuclear and electronically excited Rb*Yb molecules in a hybrid conservative trap by photoassociation of ultracold $^{87}\mathrm{Rb}$ and $^{176}\mathrm{Yb}$. The molecules are formed below the ${\mathrm{Rb}}_{5\mathit{p}1}(^{2}P_{1/2})+{\mathrm{Yb}}_{6\mathit{s}2}(^{1}S_{0})$ dissociation limit and the resonances are detected using trap-loss spectroscopy. By addressing vibrational levels with binding energies down to ${E}_{B}=\ensuremath{-}h\ifmmode\times\else\texttimes\fi{}2.2\phantom{\rule{0.16em}{0ex}}\mathrm{THz}$, we study the change in hyperfine coupling of the diatomic molecule as a function of internuclear separation. We observe a decreasing hyperfine splitting for more tightly bound excited molecular states where the hyperfine splitting is reduced by more than $30%$ compared to the atomic value for $^{87}\mathrm{Rb}$.

Physical Review AAug 3, 201615 citations

Near-threshold photoassociation of 87Rb2

M. Kemmann, Ivan Mistrík, S. Nußmann +3 more

Photoassociation of cold ${}^{87}\mathrm{Rb}{(5s,f}_{b}=2)$ atom pairs is studied within 13 GHz of the dissociation limits ${}^{87}\mathrm{Rb}{(5p}_{3/2}{,f}_{a}{)+}^{87}\mathrm{Rb}{(5s,f}_{b}=2).$ Vibrational levels in the long range, hyperfine manifolds of the ${0}_{g}^{\ensuremath{-}}$ and ${1}_{g}$ states arising from the ${}^{87}\mathrm{Rb}{(5p}_{3/2})$ fine structure limit are identified to lead to the formation of stable molecules in the photoassociation process. The vibrational bands are observed to break off, at positions matching the energetic location of potential-energy barriers predicted in the hyperfine manifolds at about 1 GHz above the ${}^{87}\mathrm{Rb}{(5p}_{3/2}{,f}_{a}{=3)+}^{87}\mathrm{Rb}{(5s,f}_{b}=1)$ dissociation limit. Empiricial potential-energy curves are derived from the data. These are found to be in agreement with predictions based on the long-range hyperfine recoupling of the excited molecular states. The selectivity of the excitation process and predissociation mechanisms are discussed.Photoassociation of cold ${}^{87}\mathrm{Rb}{(5s,f}_{b}=2)$ atom pairs is studied within 13 GHz of the dissociation limits ${}^{87}\mathrm{Rb}{(5p}_{3/2}{,f}_{a}{)+}^{87}\mathrm{Rb}{(5s,f}_{b}=2).$ Vibrational levels in the long range, hyperfine manifolds of the ${0}_{g}^{\ensuremath{-}}$ and ${1}_{g}$ states arising from the ${}^{87}\mathrm{Rb}{(5p}_{3/2})$ fine structure limit are identified to lead to the formation of stable molecules in the photoassociation process. The vibrational bands are observed to break off, at positions matching the energetic location of potential-energy barriers predicted in the hyperfine manifolds at about 1 GHz above the ${}^{87}\mathrm{Rb}{(5p}_{3/2}{,f}_{a}{=3)+}^{87}\mathrm{Rb}{(5s,f}_{b}=1)$ dissociation limit. Empiricial potential-energy curves are derived from the data. These are found to be in agreement with predictions based on the long-range hyperfine recoupling of the excited molecular states. The selectivity of the excitation process and predissociation mechanisms are discussed.

Physical Review AFeb 26, 200437 citations

Weakly bound 87 Rb 2 (5s1/2+5p1/2)1g molecules: Hyperfine interaction and LeRoy-Bernstein analysis including linear and nonlinear terms

Haikel Jelassi, Laurence Pruvost

Data on the $(5{s}_{1/2}+5{p}_{1/2}){1}_{g}$ ${}^{87}{\text{Rb}}_{2}$ state under the ${D}_{1}$ limit, provided by a photoassociation experiment on cold atoms, have been analyzed by an improved LeRoy-Bernstein (LRB) approach including linear and nonlinear terms and provide a ${c}_{6}$ value of the potential. To do that, using a model for hyperfine structure shifts, we have first subtracted the hyperfine effects in the split lines and deduced the vibrational energies. Then, we have compared three LRB-type models to fit the data. We conclude that the second-order improved LRB is well suited and allows us to deduce an experimental value of ${c}_{6}$ [${c}_{6}=(15.14\ifmmode\pm\else\textpm\fi{}0.05)\ifmmode\times\else\texttimes\fi{}{10}^{4}$ a.u.].Data on the $(5{s}_{1/2}+5{p}_{1/2}){1}_{g}$ ${}^{87}{\text{Rb}}_{2}$ state under the ${D}_{1}$ limit, provided by a photoassociation experiment on cold atoms, have been analyzed by an improved LeRoy-Bernstein (LRB) approach including linear and nonlinear terms and provide a ${c}_{6}$ value of the potential. To do that, using a model for hyperfine structure shifts, we have first subtracted the hyperfine effects in the split lines and deduced the vibrational energies. Then, we have compared three LRB-type models to fit the data. We conclude that the second-order improved LRB is well suited and allows us to deduce an experimental value of ${c}_{6}$ [${c}_{6}=(15.14\ifmmode\pm\else\textpm\fi{}0.05)\ifmmode\times\else\texttimes\fi{}{10}^{4}$ a.u.].

Physical Review AMar 20, 201410 citations

PHOTOASSOCIATION SPECTROSCOPY OF ${^{85}}Rb_{2}$ NEAR ITS DISSOCIATION LIMITPHOTOASSOCIATION SPECTROSCOPY OF ${^{85}}Rb_{2}$ NEAR ITS DISSOCIATION LIMIT

R. S. Freeland, Ph. W. Courteille, Chin‐Chun Tsai +4 more

We present results which probe the structure of ${^{85}}Rb_{2}$ very near its lowest dissociation limit. To obtain these results, we used two different variations of photoassociation spectroscopy of laser-cooled and trapped ${^{85}}Rb$ atoms. First, we have determined the positions of twelve of the highest vibrational levels of ${^{85}}Rb_{2}$ , all bound by less than $0.7 cm^{-1}$ , with two-color (free-bound-bound) photoassociation spectroscopy. The levels lie in an energy range for which singlet and triplet states are strongly mixed by the hyperfine interaction. We found that we could accurately describe these states with a novel coupled-channels inverse perturbation analysis. In a second experiment, we have carried out Zeeman-resolved photoassociation spectroscopy. This technique allowed us to probe the energy range in the lowest part of the electronic ground state continuum, which lies between the dissociation limits corresponding to different hyperfine states of the separated atoms. With this method, we have observed a Feshbach scattering resonance in the continuum for the first time, which we find can be tuned to zero energy with a magnetic field.We present results which probe the structure of ${^{85}}Rb_{2}$ very near its lowest dissociation limit. To obtain these results, we used two different variations of photoassociation spectroscopy of laser-cooled and trapped ${^{85}}Rb$ atoms. First, we have determined the positions of twelve of the highest vibrational levels of ${^{85}}Rb_{2}$, all bound by less than $0.7 cm^{-1}$, with two-color (free-bound-bound) photoassociation spectroscopy. The levels lie in an energy range for which singlet and triplet states are strongly mixed by the hyperfine interaction. We found that we could accurately describe these states with a novel coupled-channels inverse perturbation analysis. In a second experiment, we have carried out Zeeman-resolved photoassociation spectroscopy. This technique allowed us to probe the energy range in the lowest part of the electronic ground state continuum, which lies between the dissociation limits corresponding to different hyperfine states of the separated atoms. With this method, we have observed a Feshbach scattering resonance in the continuum for the first time, which we find can be tuned to zero energy with a magnetic field.

Jan 1, 19980 citations

Photoassociation of85Rb atoms into 0u+states near the 5S+5P atomic limits

T. H. Bergeman, J Qi, Dajun Wang +8 more

Journal of Physics B Atomic Molecular and Optical PhysicsSep 25, 200653 citations

Photoassociation resonances in the

{}^{87}

{}_{2}

{1}_{g}

state dissociating to

5{\phantom{\rule{0.16em}{0ex}}}^{2}S+5{}^{2}{P}_{1/2}

were produced by the excitation of colliding

{}^{87}

Rb atoms in a far-off resonance trap. Levels down to 31 cm

{}^{\ensuremath{-}1}

below the dissociation limit were measured with resonance linewidths of 15 to 20 MHz, and have been located to a one-sigma combined systematic and statistical uncertainty of 50 MHz relative to the

5{\phantom{\rule{0.16em}{0ex}}}^{2}S+5{}^{2}{P}_{1/2}

limit. Electron and nuclear spins were fixed to a space-fixed axis by circularly polarized optical pumping, so that only states with total nuclear spin

I=3

were excited, thereby greatly simplifying the spectrum. The analysis of the data yielded hyperfine coupling parameters

A(v)

, vibrational

G(v)

, and rotational

B(v)

parameters. The

G(v)

parameters could be fit to an rms accuracy of about 0.01 cm

{}^{\ensuremath{-}1}

to a potential constructed from current

{C}_{3}

and

{C}_{6}

long-range dispersion parameters plus an ab initio potential that was adjusted in depth and with quadratic terms in the internuclear distance added to the inner wall.

^{87}\mathrm{Rb}_{2}

for magnetic fields of up to

1000\phantom{\rule{0.28em}{0ex}}\text{G}

. As spectroscopic methods we use short-range photoassociation of ultracold Rb atoms as well as photoexcitation of ultracold molecules which have been previously prepared in several well-defined quantum states of the $a{\phantom{\rule{0.222222em}{0ex}}}^{3}\mathrm{\ensuremath{\Sigma}}{}_{u}^{+}$ potential. As a by-product, we present optical two-photon transfer of weakly bound Feshbach molecules into $a{\phantom{\rule{0.222222em}{0ex}}}^{3}\mathrm{\ensuremath{\Sigma}}{}_{u}^{+}$,

v=0

levels featuring different nuclear spin quantum numbers. A simple model reproduces well the molecular level structures of the $c{\phantom{\rule{0.222222em}{0ex}}}^{3}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}$ vibrational states and provides a consistent assignment of the measured resonance lines. Furthermore, the model can be used to predict the relative transition strengths of the lines. From fits to the data we extract for each vibrational level the rotational constant, the effective spin-spin interaction constant, as well as the Fermi contact parameter and the anisotropic hyperfine constant. In an alternative approach, we perform coupled-channel calculations where we fit the relevant potential energy curves, spin-orbit interactions, and hyperfine functions. The calculations reproduce the measured hyperfine level term frequencies with an average uncertainty of $\ifmmode\pm\else\textpm\fi{}9\phantom{\rule{0.28em}{0ex}}\mathrm{MHz}$, similar as for the simple model. From these fits we obtain a section of the potential energy curve for the $c{\phantom{\rule{0.222222em}{0ex}}}^{3}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}$ state which can be used for predicting the level structure for the vibrational manifold ${v}^{\ensuremath{'}}=0$ to 13 of this electronic state.

We report on the creation of ultracold heteronuclear and electronically excited Rb*Yb molecules in a hybrid conservative trap by photoassociation of ultracold

^{87}\mathrm{Rb}

and

^{176}\mathrm{Yb}

. The molecules are formed below the

{\mathrm{Rb}}_{5\mathit{p}1}(^{2}P_{1/2})+{\mathrm{Yb}}_{6\mathit{s}2}(^{1}S_{0})

dissociation limit and the resonances are detected using trap-loss spectroscopy. By addressing vibrational levels with binding energies down to ${E}_{B}=\ensuremath{-}h\ifmmode\times\else\texttimes\fi{}2.2\phantom{\rule{0.16em}{0ex}}\mathrm{THz}$, we study the change in hyperfine coupling of the diatomic molecule as a function of internuclear separation. We observe a decreasing hyperfine splitting for more tightly bound excited molecular states where the hyperfine splitting is reduced by more than

30%

compared to the atomic value for

^{87}\mathrm{Rb}

Photoassociation of cold

{}^{87}\mathrm{Rb}{(5s,f}_{b}=2)

atom pairs is studied within 13 GHz of the dissociation limits

{}^{87}\mathrm{Rb}{(5p}_{3/2}{,f}_{a}{)+}^{87}\mathrm{Rb}{(5s,f}_{b}=2).

Vibrational levels in the long range, hyperfine manifolds of the ${0}_{g}^{\ensuremath{-}}$ and

{1}_{g}

states arising from the

{}^{87}\mathrm{Rb}{(5p}_{3/2})

fine structure limit are identified to lead to the formation of stable molecules in the photoassociation process. The vibrational bands are observed to break off, at positions matching the energetic location of potential-energy barriers predicted in the hyperfine manifolds at about 1 GHz above the

{}^{87}\mathrm{Rb}{(5p}_{3/2}{,f}_{a}{=3)+}^{87}\mathrm{Rb}{(5s,f}_{b}=1)

dissociation limit. Empiricial potential-energy curves are derived from the data. These are found to be in agreement with predictions based on the long-range hyperfine recoupling of the excited molecular states. The selectivity of the excitation process and predissociation mechanisms are discussed.

Data on the

(5{s}_{1/2}+5{p}_{1/2}){1}_{g}

{}^{87}{\text{Rb}}_{2}

state under the

{D}_{1}

limit, provided by a photoassociation experiment on cold atoms, have been analyzed by an improved LeRoy-Bernstein (LRB) approach including linear and nonlinear terms and provide a

{c}_{6}

value of the potential. To do that, using a model for hyperfine structure shifts, we have first subtracted the hyperfine effects in the split lines and deduced the vibrational energies. Then, we have compared three LRB-type models to fit the data. We conclude that the second-order improved LRB is well suited and allows us to deduce an experimental value of

{c}_{6}

[${c}_{6}=(15.14\ifmmode\pm\else\textpm\fi{}0.05)\ifmmode\times\else\texttimes\fi{}{10}^{4}$ a.u.].

PHOTOASSOCIATION SPECTROSCOPY OF

{^{85}}Rb_{2}

NEAR ITS DISSOCIATION LIMIT

We present results which probe the structure of

{^{85}}Rb_{2}

very near its lowest dissociation limit. To obtain these results, we used two different variations of photoassociation spectroscopy of laser-cooled and trapped

{^{85}}Rb

atoms. First, we have determined the positions of twelve of the highest vibrational levels of

{^{85}}Rb_{2}

, all bound by less than

0.7 cm^{-1}

, with two-color (free-bound-bound) photoassociation spectroscopy. The levels lie in an energy range for which singlet and triplet states are strongly mixed by the hyperfine interaction. We found that we could accurately describe these states with a novel coupled-channels inverse perturbation analysis. In a second experiment, we have carried out Zeeman-resolved photoassociation spectroscopy. This technique allowed us to probe the energy range in the lowest part of the electronic ground state continuum, which lies between the dissociation limits corresponding to different hyperfine states of the separated atoms. With this method, we have observed a Feshbach scattering resonance in the continuum for the first time, which we find can be tuned to zero energy with a magnetic field.