1. 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 , Champaign-Urbana, Illinois Paper – RI 12

2. 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. 

3. Experimental Setup 
Schematic diagram of LIF experimental setup

4. 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 ( nm) pumped by Nd:YAG laser at 355 nm

5. Results and Analysis
Observed electronic transitions of the TaF

6. 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)

7. ___________ 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
_______________________________________________
___________ 3
___________ 2
Laser
The vibrational separation (DG1/2) for the X3Σ - state has been determined to be cm-1

8. 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

9. Molecular Constants for TaF (cm-1)
State W v Tn Bn
[22.9]
(1)
0.2644(2)
[22.1] 1
(1)
0.2630(1)
(5)
0.2665(1)
[19.9]
(4)
0.2690(1)
[19.8] 2
(5)
0.2700(1)
(4)
0.2720(1)
(5)
0.2740(1)
[18.6]
(2)
0.2744(1)
[18.1]
v +1
(1)
0.2668(1)
(7)
0.2685(1)
X 3Σ-
(1)
0.2926(1)
697.02(1)
0.2943(1)
0.2961(1)
State W v Tv Bv
[21.4] 2 1
a (6)
0.2649(1)
a (5)
0.2685(1)
A 3
a (4)
0.2821(1) a
0.2838(1)

10. 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.

11. 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

12. 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

13. 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  

14. 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)

15. 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

16. 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 cm-1

17. Comparison between theoretic calculation and experimental results
 state T0 r0
G1/2 B0
Components %
[21.4] W = 2 a
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
1.925
0.2644
(12) 0+
23608
1.901
646*
0.2712
(4)3P(75)
[22.1] W = 0
1.918
581.0
0.2665
(11) 0+
22550
1.889
623*
0.2748
(3)3S-(51) + (2)5P(13)
[19.9] W = 0
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
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
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
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)

18. 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 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

19. Thank you for your attention