Laser spectroscopy and ab initio calculations on TaF K. F. Ng and Allan S-C. Cheung Department of Chemistry, the University of Hong Kong, Hong Kong Wenli Zou Institute of Modern Physics, Northwest University, Xi’an China Wenjin Liu Department of Chemistry, Peking University, Beijing, China ISMS 71th Meeting - June 19 - 24, 2016 - Champaign-Urbana, Illinois Paper – RI 12

Background Theoretical calculation: TaCl [1] Bauschlicher (2000) J. Phys. Chem. 104, 5843 Performed DFT and CCST(T) calculations predicted the ground state to be 3+ state and several low-lying 5, 5 and 3 electronic states. TaCl [2] Bernath & coworkers (2005) J. Mol. Spectrosc. 232, 358 Experimental measurement of the TaCl spectrum. The ground and nearby low energy states were confirmed to be the Ω" = 0+ and Ω" = 2 components. 

Experimental Setup  Schematic diagram of LIF experimental setup

Experimental Conditions Molecule production: Laser ablation/reaction     Ta + SF6 (5% in Ar) → TaF + etc. Ablation Laser: Nd:YAG, 10 Hz, 532 nm, ~1.5 mJ Gas Pressure: 6 atm (argon + reagent gas) Background pressure: 8 x 10-5Torr. Excitation Laser for LIF spectroscopy: Tunable dye laser (440 -560 nm) pumped by Nd:YAG laser at 355 nm

Results and Analysis Observed electronic transitions of the TaF

Laser Induced Fluorescence spectrum of (0, 1) band of the [19 Laser Induced Fluorescence spectrum of (0, 1) band of the [19.8] W' = 0 - W'' = 0 transition J ___________ 1 ___________ 0   ___________ 2 R(0) P(1)

___________ 1 ___________ 0 ___________ 3 ___________ 2 Laser Resolved fluorescence spectrum of the (v, 0) band of the [18.0] W = 1 - X 3Σ- (0+) transition ___________ 1 ___________ 0   _______________________________________________ 4 ___________ 3 ___________ 2 Laser The vibrational separation (DG1/2) for the X3Σ - state has been determined to be 697. 02 cm-1

Laser Induced Fluorescence spectrum of (0, 1) band of the [21 Laser Induced Fluorescence spectrum of (0, 1) band of the [21.4] W' = 2 - W'' = 2 transition J ___________ 3 ___________ 2   ___________ 4 R(2) Q(2) P(3) cm-1

Molecular Constants for TaF (cm-1) State W v Tn Bn [22.9] 22937.47(1) 0.2644(2) [22.1] 1 22704.47(1) 0.2630(1)   22123.51(5) 0.2665(1) [19.9] 19856.69(4) 0.2690(1) [19.8] 2 20950.05(5) 0.2700(1) 20357.69(4) 0.2720(1) 19759.82(5) 0.2740(1) [18.6] 18626.33(2) 0.2744(1) [18.1] v +1 18672.36(1) 0.2668(1) 18093.46(7) 0.2685(1) X 3Σ- 1388.11(1) 0.2926(1) 697.02(1) 0.2943(1) 0.2961(1) State W v Tv Bv [21.4] 2 1 a + 21982.90(6) 0.2649(1)   a + 21445.21(5) 0.2685(1) A 3 a + 675.98(4) 0.2821(1) a 0.2838(1)

Ab initio calculations on TaF The low-lying Λ-S and  states of TaF were calculated: Level of theory - The state-averaged complete active space self-consistent field (SA-CASSCF) and with internally contracted multi-reference configuration interaction with singles and doubles and Davidson's cluster correction (MRCISD+Q) (with the active space of 4 electrons in 6 orbitals, that is, the molecular orbitals corresponding to Ta 5d6s are active). Spin-orbit coupling (SOC) the state-interaction approach at the SA-CASSCF level via the relativistic effective core potentials (RECPs) spin-orbit operator, where the diagonal elements of the spin-orbit matrix are replaced by the above MRCISD+Q energies. The spectroscopic properties of the ground and many low-lying electronic states of the TaF molecule were obtained.

Ab initio calculations on TaF Λ-S states of TaF 3+ (x 2) 3 (x 7) 3 (x 4) 3 (x 1) 1.6 1.8 2.0 2.2 2.4 2.6 5000 10000 35000 30000 25000 20000 15000 R (Å) Ta-F Energy (cm-1) 3- (x 5) 3 (x 5) 3 (x 2) 3 3 3 3- The three lowest energy states are 3- , 3 and 3 states

Spectroscopic constants of Λ-S states of 181Ta19F. Re ωe ωeχe Be B0 Dominant configurations 1σ/2σ/1π/1δ in CASSCF w.f. at Re's a)   (cm-1) (Å) (≥ 10%) [1]1Σ+ 6225 1.811 704.1 2.80 0.2990 0.2981 2/0/0/2 (70) + 2/0/2/0 (13) [2]1Σ+ 22306 1.886 630.7 4.08 0.2758 0.2748 1/1/0/2 (34) + 2/0/2/0 (29) + 0/0/2/2 (11) + 1/1/2/0 (10) [1]1Π 8394 1.847 682.1 2.72 0.2873 0.2865 2/0/1/1 (77) [2]1Π 20548 1.917 593.6 2.56 0.2669 0.2660 1/0/1/2 (38) + 2/1/1/0 (27) + 1/1/1/1 (16) [1]3Σ+ 20419 1.904 592.5 2.18 0.2705 0.2697 1/1/0/2 (81) + 1/0/2/1 (12) [2]3Σ+ 21905 1.916 597.5 2.73 0.2670 0.2662 1/0/2/1 (78) [1]3Σ- 1.804 720.1 2.88 0.3012 0.3003 2/0/0/2 (71) + 1/1/0/2 (16) [2]3Σ- 9428 1.905 630.0 2.57 0.2702 0.2694 2/0/2/0 (71) + 1/0/2/1 (13) [3]3Σ- 19126 1.867 648.8 2.54 0.2814 0.2806 1/1/0/2 (74) + 2/0/0/2 (16) [4]3Σ- 23229 1.919 600.8 2.67 0.2661 0.2653 1/0/2/1 (54) + 2/0/0/2 (13) + 2/0/2/0 (12) [5]3Σ- 26081 1.907 576.7 2.36 0.2696 0.2687 1/1/0/2 (82) [1]3Π 3988 1.850 680.8 0.2857 2/0/1/1 (72) + 1/0/1/2 (18) [2]3Π 15219 1.915 578.0 2.41 0.2674 0.2666 2/1/1/0 (39) + 1/0/1/2 (30) + 0/1/1/2 (11) [3]3Π 17209 1.880 640.6 0.2775 0.2767 1/0/1/2 (79) + 1/0/3/0 (11) [4]3Π 20087 1.890 606.2 2.94 0.2745 0.2736 1/0/1/2 (67) + 0/1/1/2 (13) + 1/1/1/1 (11) Lowest [3]3 19657 1.919 642.7 2.89 0.2662 0.2657 1/0/2/1 (56) + 1/0/0/3 (17) + 2/1/0/1 (13) [4]3 22947 1.936 590.1 2.23 0.2615 0.2608 1/0/2/1 (89) [5]3 28590 1.898 638.6 3.99 0.2722 0.2714 1/0/2/1 (45) + 1/0/0/3 (19) + 1/2/0/1 (15) + 0/1/0/3 (10) [1]3Φ 2985 1.849 686.8 2.65 0.2867 0.2859 2/0/1/1 (87) [2]3Φ 17749 1.875 628.9 2.73 0.2789 0.2781 1/0/1/2 (72) + 1/1/1/1 (18) [3]3Φ 24683 1.935 576.7 2.76 0.2618 0.2609 1/1/1/1 (81) [4]3Φ 26501 1.966 547.8 2.07 0.2537 0.2529 1/1/1/1 (79) + 0/1/1/2 (13) 2nd Lowest  

Molecular orbital diagram Dominating electronic configuration gives rise to the ground state of TaF : 1σ21π42σ21d2 ==> X 3Σ- Major electronic configuration gives rise to the second lowest state of TaF : 1σ21π42σ21d12π1 ==> 3 Calculated separation between the two states is 2985 cm-1  

3 3S- Spin-orbit components (ab initio calculations) Labelled by Λ-S states Labelled by  values only  = 4 34 3 1784 cm-1  = 3 33 3308 cm-1 2985  = 1 (3S1- ) 32  = 2 1786 cm-1 3S-  = 0 (3S0- ) (Ground state)   (3S1- doubly degenerate)

Ab initio calculations on TaF  states of TaF 10000 20000 30000 40000 =0+ (x 20) =2 (x 27) 1.6 1.8 2.0 2.2 2.4 2.6 Energy (cm-1) R (Å) Ta-F  = 0  = 2 The two lowest energy states are  = 0 and  = 2 states The  = 0 component is from the 3S0- and  = 2 is from the 32

Calculated separation between the two lowest states is 1650 cm-1 Ω States a Te Re ωe   ωeχe Be B0 Dominant Λ-S states at Re's (cm-1) (Å) (≥ 10%) [1]0+ 1.811 701.3 1.69 0.2989 0.2980 [1]3Σ- (73) + [1]1Σ+ (14) + [1]3Π (12) [2]0+ 4002 1.866 631.9 2.31 0.2815 0.2806 [1]5Π (43) + [1]3Π (35) [3]0+ 6919 1.861 662.9 3.52 0.2831 0.2822 [1]3Π (45) + [1]5Π (38) [4]0+ 9212 1.895 Anharmonic [1]5 (55) + [1]1Σ+ (15) + [2]3Σ- (13) [5]0+ 9738 1.884 683.8 5.36 0.2759 0.2743 (44) + [1]1Σ+ (23) + [2]3Σ- (11) [6]0+ 11569 1.869 732.0 2.62 0.2799 [2]3Σ- (55) + [1]1Σ+ (25) [7]0+ 16659 1.908 573.2 1.61 0.2694 0.2687 [2]3Π (70) + [2]3Σ- (11) [8]0+ 19208 1.896 597.2 3.21 0.2727 0.2714 [3]3Π (41) + [3]3Σ- (22) + [2]5Π (16) + [5]3Π (10) [1]2 1650 1.851 680.6   2.72 0.2863 0.2855 [1]3Φ (91) [2]2 5390 1.867 622.4 2.53 0.2812 0.2803 [1]5Π (44) + [1]3Π (38) [3]2 7249 1.865 667.2 3.32 0.2818 0.2810 [1]3Π (52) + [1]5Π (32) [4]2 10235 1.912 599.4 2.22 0.2681 0.2675 [1]5 (61) + [1]5Σ- (13) [5]2 11464 1.886 610.3 2.48 0.2757 0.2747 [1]5Σ- (30) + [1]1 (28) + [1]3 (17) [6]2 11722 1.890 640.2 2.80 0.2746 0.2738 [1]5Σ- (38) + [1]3 (24) + [1]5 (12) [7]2 13800 1.872 628.8 5.59 0.2797 0.2788 [1]3 (41) + [1]1 (37) [8]2 15992 1.946 562.4 0.52 0.2593 0.2585 [1]5Φ (77) [1]1 1786 1.810 698.4 1.86 0.2993 0.2984 [1]3Σ- (94)   [2]1 3380 1.861 636.4 2.77 0.2831 0.2821 [1]3Π (45) + [1]5Π (23) + [1]1Π (12) [3]1 5031 1.871 643.1 2.24 0.2802 0.2794 [1]5Π (71) + [1]3Π (10) [4]1 6077 1.870 642.5 2.50 0.2805 0.2797 [1]5Π (67) [5]1 9222 1.912 600.3 2.58 0.2682 0.2675 [1]5 (58) + [1]5Φ (11) [6]1 11133 1.886 587.6 0.55 0.2753 0.2745 [2]3Σ- (27) + [1]3 (25) + [1]3Π (20) [7]1 11350 1.891 657.2 5.82 0.2742 0.2732 [1]3 (44) + [2]3Σ- (29) + [1]5 (10) [8]1 11891 599.4 1.44 0.2743 0.2737 [1]5Σ- (59) + [1]5Π (17) [9]1 12630 1.865 678.7 6.40 0.2817 [1]1Π (55) + [1]3 (11) [10]1 14723 1.945 556.2 0.50 0.2596 0.2581 [1]5Φ (77) Calculated separation between the two lowest states is 1650 cm-1   Calculated spin-orbit separation between the is  = 0 and  = 1 components 1786 cm-1

Comparison between theoretic calculation and experimental results  state   T0 r0 G1/2 B0 Components % [21.4] W = 2 a + 21982.90 1.911 537.7 0.2685 (16) 2 23170 1.912 666* 0.2681 (4)3P(33) + (2)5P(25) + (2)3P(11) + (2)3D (11) [22.9] W = 0 22937.47 1.925 0.2644 (12) 0+ 23608 1.901 646* 0.2712 (4)3P(75) [22.1] W = 0 22123.51 1.918 581.0 0.2665 (11) 0+ 22550 1.889 623* 0.2748 (3)3S-(51) + (2)5P(13) [19.9] W = 0 19856.69 1.909 0.2690 (10) 0+ 21582 1.924 587* 0.2649 (5)3P(53) + (2)5P(11) + (4)3S-(10) [19.8] W = 0 19759.82 1.891 597.9 0.2740 (9) 0+ 20151 1.900 626* 0.2715 (3)3P(39) + (2)5P(37) + (5)3P(16) [18.6] W = 0 18626.33 1.890 0.2744 (8) 0+ 19208 597* 0.2714 (3)3P(41) + (3)3S-(22) + (2)5P(16) + (5)3P (10) [18.1] W = 1 18093.46 578.9 (12) 1  18516 1.908 594* 0.2693 (3)3P(39) + (2)3P(33) A3F2 a 1.864 676.0 0.2821 (1) 2 1650 1.853 681* 0.2855 (1)3F(91) X3S- 1.819 697.0 0.2961 (1) 0+ 1.814 701* 0.2980 (1)3S-(73) + (1)1S+(14) + (1)3P(12)

Summary The TaF molecule has been studied experimentally for the first time. The molecular properties of the ground X3S0- state of TaF were determined: bond length 1.8190 Ǻ Detailed ab initio calculations with SOC has been performed and the results agree quite well with experimental determinations The ground state has a dominating electronic configuration (73%) 1σ21π42σ21d2

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