1. Double Resonance in the Rubidium Dimer : the 2 1  g state. A. Drozdova*, A.-R. Allouche, G. Wannous, P. Crozet and A.J. Ross Institut Lumière Matière, Université Lyon1 & CNRS UMR5306, Villeurbanne, France * Current address : Institute of Oceanology of the Russian Academy of Sciences (IO RAS), Moscow, Russia.

2. 2  Ti:sa OODR (940 + 885 nm) to reach 2 1  g Resolved fluorescence to B 1  u and A 1  u + Reported by Amiot et al. (1997) but not assigned. PLS excitation spectra reported by Han et al. (2012) T' from E (A,b) + laser 2.  T' = 0.03 cm -1 Step 1 is STRONG. A-X fluorescence is STRONG, is excited by both lasers and hides useful transitions. A  X 2 1  g  A SO mixing

3. 2 1  g – B 1  u Fluorescence patterns FCF => v' = 3. Observe many J' in one spectrum. Analyse relaxed bands 0<v"<20 Collisions :  J even e-e, f-f,  J odd e-f cm -1  v = -1 Res 0.05 cm -1 20 mins J' 87 e, via R(85) A-X R(86) 2 1  g -A 2  >1  m filters

4. Observations & analysis This work : 85 Rb 2, 85 Rb 87 Rb Extended observations for 2 1  g state.  fluo ~ 0.005 cm -1. PLS Han et al. 85 Rb 2, 85 Rb 87 Rb CPL 538 1-4 2012 T' ~ 0.03 cm -1. T vJ (A ) +  laser FT-LIF Amiot et al. 85 Rb 2, 85 Rb 87 Rb CPL 274 91-98 (1997) PRL 83 2316-19 (1999) T' ~ 0.01 cm -1. T vJ (X ) + 2 laser Analysis OK except … Lit. G v, B v at low v in B 1  u Some local perturbations in 2 1  g 1450 term values from ~11000 lines

5. Number crunching : Least squares fits Dunham fit : up to v = 55. 'Robust' weighting reduces effect of local perturbations in v 17-20, where shifts reach 0.15 cm -1 11020 transitions, Weighted RMS dev. = 0.74 (unweighted, 0.015 cm -1 ) RKR potential + ab initio V(R) to guide at large R 2 1  g dissociates to Rb(5s) + Rb(4d) MLR Potential fit : up to v = 63 (far fewer data for v > 55) 'Robust' weighting rejected 11048 transitions (defining ~1450 T vJ ) Weighted RMS dev. 1.9

6. "Morse + Long Range" analytical potential curve DPotFit 2.0, R.J. Le Roy U. Waterloo Chem.Phys. Research report 667 (2013) Here, I have 14  parameters, and take p = 4 and q = 5. Constraints on D lim = D e (X)+E (Rb 4D 3/2 ) Constraints on C 5, C 6 for Rb(5s) + Rb(4d) Dalgarno & Marinescu PRA 52 311-328 (1995)

7. What does the Morse/Long-Range PEC look like? Constraints T e 22069.2 cm -1 D lim 23349.28 cm -1 R e 5.2462 Å

8. Extrapolation beyond the data range Not absurd (OK, not perfect either) Possible check : Plot of C 5_eff vs 1/R. Slope = C 6_eff R (Å) Extrapolation Imposed limit Outer turning points v = 55 9.85 Å (OK) v = 60 10.5 Å v = 64 11.2 Å

9. How does it fit in with other states ? Hard to be sure of highest level assignments. Other states are close by. 3 1  g + 2 3  g +,1 3  g  3 3  g 1 1  g, 1 3  g share 5s + 4d parents 2 1  g 3 3  g + 2 3  g + 3 1  g + 4 1  g + 3 3  g 1 3  g

10. Remarks This work has 'sorted out' one of the 5s + 4d states of Rb 2. Inner wall crossing causes some local perturbations Uppermost section not yet well defined. Acknowledgements Spectral archives from C. Amiot, Lab. Aimé Cotton Orsay Funding for A. Drozdova MAE & Eiffel scholarship Inexhaustible enthusiasm & advice on DPotFit from RJ Le Roy