The optical spectrum of SrOH revisited: Zeeman effect, high- resolution spectroscopy and Franck- Condon factors TRUNG NGUYEN, DAMIAN L KOKKIN, TIMOTHY STEIMLE Department of Chemistry & Biochemistry, Arizona State University, Tempe, AZ, USA IVAN KOZYRYEV, JOHN M. DOYLE Department of Physics, Harvard University, Cambridge, MA, USA.

Outline Motivation Experimental setups Low resolution: dispersed fluorescence & calculation of FCFs High-resolution: Zeeman spectroscopy of B 2  + -X 2  + and A 2  -X 2  + Analysis of the Zeeman effect

Motivation  Supporting spectroscopy for Magneto Optical Trapping (MOT) experiments being conducted by Professor Doyles’ group.  Required information : 1) Magnetic g-factors for the X 2 Σ +, A 2 Π, B 2 Σ states 2) The branching ratios/ Franck – Condon factors Sr-O O-H

Relevant previous spectroscopic studies  X 2  + (SrOH & SrOD) Pure rotational spectra: Anderson et al (1992), Ziurys’s group; Spectroscopic parameters for X 2   OODR B´ 2 Σ + ‒ A 2 Π, D 2 Σ + ‒ A 2 Π: Wang et al (2007) (Bernath’s group) Combined analysis of microwave, optical OODR Spectroscopic parameters for A 2 Π +, B´ 2 Σ +, C 2 Π + and D 2 Σ +  B 2  + – X 2  + Nakagawa et al. (1983)  Optical Stark A 2 Π ‒ X 2  +, B 2 Σ + ‒ X 2  + : Steimle et al. (1992) OODR Doppler Limited No analysis of high resolution field-free spectrum There is a need for improved parameters for the A 2 Π and B 2 Σ + states!

0.5’’ Sr rod Ablation laser Supersonic expansion Pulsed valve Supersonic expansion source Generation via laser ablation/supersonic expansion Production of SrOH: Ablated Sr + Ar(98%)/CH 3 OH(2%)

Exp. Set-up (cont.) a) Dispersed Fluorescence λ ex Grating Mirror Entrance Slit 2D –CCD 2/3 m Monochromator Supersonic Expansion Pulsed or cw dye laser light The use of the intensified CCD, which samples a wide spectral region simultaneously, is essential for accurate branching ratio measurements. (i.e. elimination of pulse-to-pulse variation in production of SrOH.

Well collimated molecular beam Rot.Temp.<10 K Single freq. tunable laser radiation skimmer Ablation laser CH 3 OH or H 2 O 2 Magnetic assembly Optical Zeeman Spectroscopy PMT Gated photon counter LIF CW dye laser Molecular beam Sr rod Pulse valve b) High-resolution optical Zeeman spectroscopy

Observations: Dispersed Fluorescence of Sr-O O-H excite fluoresce DF wavelength (nm) CCD Counts Metastable Sr emission  Branching Ratios: = No evidence of : or = Using CW laser excitation

Observations: Dispersed Fluorescence of Sr-O O-H excite fluoresce DF wavelength (nm) CCD Counts  Branching Ratios: Sr emission SrOH A 2  1/2 -X 2  + Laser ASE No evidence of : or = = Using pulsed laser excitation

Observations: Dispersed Fluorescence of Sr-O O-H excite fluoresce DF wavelength (nm) CCD Counts  Branching Ratios: Metastable Sr emission No evidence of : or SrOH A 2  3/2 -X 2  + Laser ASE = Using pulsed laser excitation = 0.957

TransitionCalculated FCFsObserved branching ratio B 2  + (000) -- X 2  + (000) B 2  + (000) -- X 2  + (100) A 2   (000)-- X 2  + (000) A 2   (000) -- X 2  + (100) A 2   (000) -- X 2  + (000) A 2   (000) -- X 2  + (100) Comparison with I. Kozyryev’s (Doyle-group) predicted FCFs

Observations: Zeeman low-J P Q 12, P 1,& P 2 branch features of B 2  + –X 2  + P 1 (1) P 2 (2)Q 12 (1) Field-Free Obs. 970 G, Perpendicular Pol. Predicted 0 G to 970 G, Perp. Pol.

Observations: Zeeman low-J R Q 21, S R 21,& R 2 branch features of A 2    –X 2  + Field-Free Obs G, Parallel Pol. Predicted 0 G to 2785 G, Parallel. Pol. R Q 21 (3) S R 21 (0) R Q 21 (1) R 2 (1) R Q 21 (2)

Observations: Zeeman low-J P Q 12, & Q 1 R 12 branch features of A 2    –X 2  + Field-Free Obs G, Perpendicular Pol. Predicted 0 G to 2848 G, Perp. Pol. Q 12 (0)

In the Hund’s case (a) limit these levels would not tune. Splitting very nearly equal to that expected for a “free” electron : 2  B  B z where  B is the Bohr magneton=1.399 MHz/G. A small parity dependence due to interaction with the B 2   state. Magnetic tuning of energy levels associated with the Q 12 line  -dbl.

Effective Hamiltonian Modelling the Spectra a)g S and g L ’ need to be viewed as variables (i.e. allowed to vary from their nominal values of & 1.000). b)The g l & g l ’ are small terms introduced to account for mixing with other electronic states. Zeeman terms Needed for the H hyperfine in X 2  + state Curl relationships (after Prof. Curl)

Zeeman’s effect measurements and g-factor fitting results ConstantX 2 Σ + (000)B 2 Σ + (000)A 2 Π (000) T (3) (11) A (30) B (17) (4) D(×10 -7 ) gamma (11)_ A D (×10 -7 ) p+2q (12) q(×10 -4 ) RMS Zeeman parameters gLgL _1.000 gSgS glegle (16) 0.00 g l’ (6) RMS

Summary The transition wavelengths and magnetic tuning of the low-J lines of the B 2  + -X 2  + and A 2  -X 2  + states that will be used in the MOT experiment have been measured The g-factors and field-free parameters have been precisely determined. Branching ratios have been experimentally determined and generally agree with predicted FCFs

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