Vibrational quenching of the electronic ground state in ThO in cold collisions with $^{3}\mathrm{He}$

Vibrational quenching of the electronic ground state in ThO in cold collisions with ${}^{3}{He}$

Yat Shan Au, Colin B. Connolly, Wolfgang Ketterle, and John M. Doyle

Phys. Rev. A 90, 032703 – Published 3 September 2014

Abstract

We measure the ratio $γ$ of the momentum transfer–to–vibrational quenching cross section for molecular thorium monoxide (ThO) [ $X (^{1} Σ^{+})$ , $v = 1$ , $J = 0$ ] in collisions with atomic helium between 800 mK and 2.4 K. We find $γ \sim 10^{4}$ . We also observe indirect evidence for ThO-He van der Waals complex formation, which has been predicted by theory [Tscherbul, Sayfutyarova, Buchachenko, and Dalgarno, J. Chem. Phys. 134, 144301 (2011)], and in conjunction, we determine the three-body recombination rate constant at 2.4 K, $Γ_{3} = 8 \pm 2 \times 10^{- 33}$ ${cm}^{6}$ $s^{- 1}$ .

Received 20 March 2014

DOI:https://doi.org/10.1103/PhysRevA.90.032703

Authors & Affiliations

Yat Shan Au^1,3, Colin B. Connolly^1,3, Wolfgang Ketterle^2,3, and John M. Doyle^1,3,*

¹Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
²Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
³Harvard-MIT Center for Ultracold Atoms, Cambridge, Massachusetts 02138, USA

^*doyle@physics.harvard.edu

Properties of the ground $^{3} F_{2}$ state and the excited $^{3} P_{0}$ state of atomic thorium in cold collisions with ${}^{3}{He}$

Yat Shan Au, Colin B. Connolly, Wolfgang Ketterle, and John M. Doyle

Phys. Rev. A 90, 032702 (2014)

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Vol. 90, Iss. 3 — September 2014

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Figure 1
Optical density (OD) decay of ThO in its X ( $v = 0$ , $J = 0$ ) state at a high helium density ( $n_{He} = 3 \times 10^{16}$ ${cm}^{- 3}$ ) and 2.4 K (single shot). The solid (red) line is fit to a sum of two exponentials corresponding to ThO loss to diffusion and to vdW molecule formation. We verify that both diffusion modes and temperature stabilize within the first 50 ms by observing decay of atomic chromium produced simultaneously (not shown). The apparent oscillation visible at late times (small OD) is caused by mechanical vibration of the apparatus, and it has no significant effect on the early-time (large-OD) fitted lifetime.
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Figure 2
Relevant energy levels of the ThO molecule. Letters refer to the electronic states, X ( $^{1} Σ^{+}$ ) and C (77% $^{1} Π$ , 20% $^{3} Π$ ), respectively. All measurements were performed in the ground rotational levels, $J = 0$ for the X state and $J = 1$ for the C state. Optical pumping via the X ( $v = 0) \to C$ ( $v = 1$ ) R(0) transition at 650 nm is used to transfer the population to the X ( $v = 1$ ) state, which is probed using the X ( $v = 1) \to C$ ( $v = 1$ ) R(0) transition at 690 nm. The relative scale of ThO-He bound-state energies is also shown.
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Figure 3
Fits to early- and late-time decay-time constants $τ_{s}$ and $τ_{l}$ in Eq. (4) and Eq. (5) at various helium densities at 2.4 K. Open squares (filled circles) denote fitted values for $τ_{l}$ ( $τ_{s}$ ). The dashed black line and solid (red) line are fits to Eq. (5) and Eq. (4), respectively, where the diffusive rate constants in Eq. (2) are extracted.
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Figure 4
Optical density (OD) of ThO in its X ( $v = 1$ , $J = 0$ ) state at 1.2 K (single shot). The initial OD, produced by molecule production via laser ablation, varies in both magnitude and duration and therefore it is unsuitable for the study of vibrational quenching. Instead, at 50 ms, a short optical pumping pulse [shaded (gray) area] transfers the population from the X ( $v = 0$ , $J = 0$ ) state. This method removes noise from shot-to-shot fluctuation. The solid (red) line at the right is a fit to a single-exponential decay.
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Figure 5
Observed vibrational quenching of the X ( $v = 1$ , $J = 0$ ) state of ThO at 1.2 K. Error bars are statistical uncertainties. The ${}^{3}{He}$ density is determined from the diffusive decay of Cr produced simultaneously [23]. The solid (red) line is a combined diffusion, two-body, and three-body fit to the data [Eq. (7)]. The dashed black line is a three-body fit. The effect of diffusion is insignificant for $n_{He} ≳ 1.2 \times 10^{16}$ ${cm}^{- 3}$ .
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Figure 6
Collisional quenching of the first vibrationally excited state of ThO in collisions with ${}^{3}{He}$ . Shown is the ratio $γ$ of the momentum transfer to the vibrational quenching cross section for the X ( $^{1} Σ^{+}$ ), $v = 1$ , $J = 0$ state versus the temperature.
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Physical Review A

covering atomic, molecular, and optical physics and quantum information

Vibrational quenching of the electronic ground state in ThO in cold collisions with ${}^{3}{He}$

Yat Shan Au, Colin B. Connolly, Wolfgang Ketterle, and John M. Doyle

Phys. Rev. A 90, 032703 – Published 3 September 2014

Abstract

Authors & Affiliations

See Also

Properties of the ground $^{3} F_{2}$ state and the excited $^{3} P_{0}$ state of atomic thorium in cold collisions with ${}^{3}{He}$

Yat Shan Au, Colin B. Connolly, Wolfgang Ketterle, and John M. Doyle

Phys. Rev. A 90, 032702 (2014)

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Physical Review A

covering atomic, molecular, and optical physics and quantum information

Vibrational quenching of the electronic ground state in ThO in cold collisions with He3

Yat Shan Au, Colin B. Connolly, Wolfgang Ketterle, and John M. Doyle

Phys. Rev. A 90, 032703 – Published 3 September 2014

Abstract

Authors & Affiliations

See Also

Properties of the ground 3F2 state and the excited 3P0 state of atomic thorium in cold collisions with He3

Yat Shan Au, Colin B. Connolly, Wolfgang Ketterle, and John M. Doyle

Phys. Rev. A 90, 032702 (2014)

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Vibrational quenching of the electronic ground state in ThO in cold collisions with ${}^{3}{He}$

Properties of the ground $^{3} F_{2}$ state and the excited $^{3} P_{0}$ state of atomic thorium in cold collisions with ${}^{3}{He}$