Physical Review Letters

Long-Range Predissociation in Two-Color Photoassociation of Ultracold Na Atoms

Peter Molenaar, P. van der Straten, H G M Heideman

Published Aug 19, 1996• 37 citations

Abstract

We report two-color photoassociative ionization of sodium in a magneto-optical trap. The experimental results yield information on both singly and doubly excited states. We find that the highest bound vibrational levels ( $v>20$) of the singly excited ${0}_{g}^{\ensuremath{-}}$ state predissociate into the ${3}^{2}{P}_{3/2}{+3}^{2}{S}_{1/2}({F}_{g}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1)$ dissociation continuum due to avoided crossings of the hyperfine components of this potential with other molecular symmetries. Based on symmetry and energy consideration we argue that a doubly excited ${1}_{u}$ state remains autoionizing even when excited only a few GHz above the dissociation continuum.

DOI: 10.1103/physrevlett.77.1460

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Physical Review Letters

Long-Range Predissociation in Two-Color Photoassociation of Ultracold Na Atoms

Peter Molenaar, P. van der Straten, H G M Heideman

Published Aug 19, 1996• 37 citations

Publisher

Abstract

v>20

) of the singly excited

{0}_{g}^{\ensuremath{-}}

state predissociate into the

{3}^{2}{P}_{3/2}{+3}^{2}{S}_{1/2}({F}_{g}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1)

dissociation continuum due to avoided crossings of the hyperfine components of this potential with other molecular symmetries. Based on symmetry and energy consideration we argue that a doubly excited

{1}_{u}

state remains autoionizing even when excited only a few GHz above the dissociation continuum.

DOI: 10.1103/physrevlett.77.1460

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Arjen Amelink, K. M. Jones, Paul D. Lett +2 more

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Photoassociation of atoms in ultracold collisions probed by wave-packet dynamics

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Observation and analysis of the hyperfine structure of near-dissociation levels of the NaCs cΣ+3 state below the dissociation limit 3S1/2+6P3/2

Wenliang Liu, Jizhou Wu, Jie Ma +4 more

We report photoassociation (PA) of ultracold Na and Cs atoms in a dual-species magneto-optical trap. Trap loss spectroscopy of the ultracold polar NaCs molecules formed by PA, which carries information about relative PA transition strengths, has been experimentally obtained by using highly sensitive modulation spectroscopy technique. The fine and hyperfine effects at near-dissociation levels of NaCs molecular $c\phantom{\rule{0.16em}{0ex}}^{3}\mathrm{\ensuremath{\Sigma}}^{+}$ state are observed and modeled. The interaction Hamiltonian is described in terms of the Hund's case ( $a$ ) coupling scheme. The molecular hyperfine structure of near-dissociation levels is simulated within a simplified model of four interacting vibrational levels belonging to different initially unperturbed electronic states. The results of the simulation infer that the interaction parameters of the observed near-dissociation levels are close to the asymptotic parameters of the pair of atoms. The coupling of the electronic states is essential for forming the hyperfine structure.We report photoassociation (PA) of ultracold Na and Cs atoms in a dual-species magneto-optical trap. Trap loss spectroscopy of the ultracold polar NaCs molecules formed by PA, which carries information about relative PA transition strengths, has been experimentally obtained by using highly sensitive modulation spectroscopy technique. The fine and hyperfine effects at near-dissociation levels of NaCs molecular $c\phantom{\rule{0.16em}{0ex}}^{3}\mathrm{\ensuremath{\Sigma}}^{+}$ state are observed and modeled. The interaction Hamiltonian is described in terms of the Hund's case ($a$) coupling scheme. The molecular hyperfine structure of near-dissociation levels is simulated within a simplified model of four interacting vibrational levels belonging to different initially unperturbed electronic states. The results of the simulation infer that the interaction parameters of the observed near-dissociation levels are close to the asymptotic parameters of the pair of atoms. The coupling of the electronic states is essential for forming the hyperfine structure.

Physical Review ASep 30, 201622 citations

v>20

) of the singly excited

{0}_{g}^{\ensuremath{-}}

state predissociate into the

{3}^{2}{P}_{3/2}{+3}^{2}{S}_{1/2}({F}_{g}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1)

{1}_{u}

state remains autoionizing even when excited only a few GHz above the dissociation continuum.

We have measured the rate of production of

{\mathrm{Na}}_{2}^{+}

ions in collisions of ultracold Na atoms held in a magneto-optical trap (MOT) as a function of probe laser detuning using a single-color probe beam. The ion rate is measured with the atoms mainly in the

3S(f=2)

level (``bright MOT'') or the

3S(f=1)

level (``dark MOT''). Using recent experimental information about the doubly excited autoionizing states of

{\mathrm{Na}}_{2},

we find that the large structures in the first 5 GHz red of the atomic transition frequency are due to a doubly resonant excitation process with levels in the ${0}_{g}^{\ensuremath{-}}$ potential (asymptotically connected to

{3S}_{1/2}{+3P}_{3/2})

as the intermediate states, and levels in the ${0}_{u}^{\ensuremath{-}}$ and

{1}_{u}

potentials (asymptotically connected to

{3P}_{3/2}{+3P}_{3/2})

as the final autoionizing states. We can account for nearly all of the observed structure in this region of the spectra for both the bright and dark MOT.

We have performed photoassociation spectroscopy to study the doubly excited states of

{\mathrm{Na}}_{2}

involved in the associative ionization of colliding

\mathrm{Na}(3P)

atoms. Rovibrational levels of two doubly excited potentials connected to the

{P}_{3/2}{+P}_{3/2}

asymptote, one of ${0}_{u}^{\ensuremath{-}}$ and one of

{1}_{u}

symmetry, have been identified. These two doubly excited potentials dominate the route to ionization used in photoassociation experiments of cold Na. Binding energies and rotational constants for all the vibrational levels with binding energies

<50\mathrm{GHz}

have been measured. The asymptotic potentials and short-range ionization probabilities are extracted from the data.

We have observed the spectrum of long range molecular states of singly excited

{\mathrm{Na}}_{2}

formed by photoassociation during ultracold associative ionization collisions of laser-cooled Na atoms. The low kinetic energy of the collision allows us to obtain very high resolution spectra and to observe states close to the dissociation limit. The spectrum shows regular vibrational series characteristic of the 1/

{\mathit{R}}^{3}

long range portion of the

{1}_{\mathit{g}}

potential (asymptotically

{\mathit{S}}_{1/2}

{\mathit{P}}_{3/2}

) as well as molecular hyperfine structure within these peaks. We extract potential parameters and compare with recent theory.

^{2}

S)+

{\mathrm{Na}}^{\mathrm{*}}

^{2}

{\mathit{P}}_{3/2}

) dissociation limit have been obtained by monitoring an enhanced

{\mathrm{Na}}_{2}^{+}

ion signal. We propose the use of pump-probe techniques to study the dynamics of the ionization process. At very large distances (typically 70 a.u.) two colliding Na atoms absorb a photon and form a coherent vibrational wave packet. We follow the packet in time and probe two possible mechanisms that are proposed to yield molecular ions: photoionization, where the second photon is absorbed at a small internuclear distance R directly ionizing the molecule, and associative ionization with excitation at intermediate R to the nuclear continuum of a doubly excited state followed by a half collision and autoionization at small R. The latter event can also lead to dissociation of the complex. The two mechanisms lead to distinct differences in the ion signals as a function of delay time between the pump and the probe pulses. Estimates of the ion rates to be expected in actual pump-probe experiments are given, which tend to favor the autoionization mechanism as the dominant reaction path.

a

) coupling scheme. The molecular hyperfine structure of near-dissociation levels is simulated within a simplified model of four interacting vibrational levels belonging to different initially unperturbed electronic states. The results of the simulation infer that the interaction parameters of the observed near-dissociation levels are close to the asymptotic parameters of the pair of atoms. The coupling of the electronic states is essential for forming the hyperfine structure.