66 th OSU International Symposium on Molecular Spectroscopy

66 th OSU International Symposium on Molecular Spectroscopy Laser Induced fluorescence Spectroscopy of Co. B H. F. Pang, Y. W. Ng and A. S-C. Cheung Department of Chemistry University of Hong Kong June 2011

Acknowledgments This work was supported by a grant from the Research Grants Council of The Government of the Hong Kong Special Administrative Region (HKU 701008). We would also like to thank Mr. P. M. Yeung for technical assistance

Interests in transition metal borides (TMB): 1. Catalysts for : 2. - hydrogenation of alkenes and alkynes 3. - reduction of functional groups 4. - deoxygenation reaction 5. 2. Remarkable physical properties: - high conductivity (Ti. B 2) - superconductivity (Mg. B 2) - super hardness (Re. B 2)

Interests in transition metal monoborides (MB): 1. Spectroscopic interest molecular & electronic structure synthesizing metal boride in gas-phase 2. Theoretical calculations limited theoretical work has been performed on MB

Introduction Theoretical calculations: • Tzeli and Mavridis (JCP 128 034309 (2008)) Using MRCI/4 Z level of theory calculated the ground state symmetry and spectroscopic properties of the 3 d transition metal monoborides ranging from Sc to Cu: Co. B X 3 state re = 1. 696 Å e =757 cm-1 No experimental observation on Co. B so far

Experimental conditions Laser ablation/reaction free jet expansion Molecule production: Co + B 2 H 6 (0. 5% in Ar) → Co. B + etc. Ablation Laser : Nd: YAG, 10 Hz, 532 nm, 5 m. J Free Jet Expansion : i) backing pressure: 6 atm B 2 H 6 (0. 5% in Ar) ii) background pressure: 1 x 10 -5 Torr LIF spectrum in the visible region Laser system: Pulsed dye lasers

Experiment

Results and Discussion => => Broadband spectrum of Co. B

Results and Discussion Laser 3 3 4 ’ = 3 – ” = 3 transition of Co. B

V” = 3 V” = 1 18296 band V” = 2 Results and Discussion Laser Resolved fluorescence spectrum of ’ = 3 – ” = 3

Results and Discussion 2 2 3 ’ = 2 – ” = 2 transition of Co. B

Results and Discussion V” = 1 V” = 2 18927 band Laser Resolved fluorescence spectrum ’ = 2 – ” = 2

This Work The analysis of the ’ = 3 – ” = 3 and ’ = 2 – ” = 2 in the spectral region between 490 and 560 nm Over 36 bands have been recorded analyzed - the electronic states are in case (c) coupling scheme (the pattern is similar to Co. O) - large linewidth => less accurate B values - isotopic bands are far away (not easy to associate)

Upper state Lower state [18. 1]3Π 2 X 3 2 =2 [18. 3]3 3 =3 X 3 2 X 3 3 v v o B B 0 0 18187. 57 0. 4914 0. 6306 0 1 17452. 89 0. 4914 0. 6239 0 0 19017. 12 0. 4896 0. 6304 0 0 19027. 50 0. 5308 (0. 5307)* 0. 6794 (0. 6802) 0 0 18251. 99 0. 4909 0. 6254 1 0 18714. 80 0. 4818 2 0 19160. 88 0. 4782 3 0 19585. 42 0. 4577 2 1 18429. 22 0. 4783 0. 6213 0 0 18596. 40 0. 4874 0. 6258 0 0 18603. 61 0. 5344 (0. 5310) 0. 6757 (0. 6778) Remarks G 1/2 = 734. 68 Co 10 B G 1/2 = 731. 66 Co 10 B Molecular Constants for the observed states of Co. B (cm-1)

Results and Discussion Vibrational bands observed for Co. B

Electronic configuration Co. B Co B 10σ σ 3 d 4 s π σ δ 4π 9σ 1δ σ π 3π 8σ 2 p

Electronic configurations Since there is = 3 substate Co. B 8 2 3 4 1 3 9 1 (10 e) 1 3 1 , 3 i Assignment of ground state X 3 3 Electronic configuration for the ground state of Co. B (1) 8 2 3 41 3 9 1 state) (2) 8 2 3 41 3 4 1 states) 1 , 3 (Ground i 1 , 3 , 1 , 3 (Excited i i

Electronic configurations Co. B 8 2 3 4 1 3 9 1 (X 3 i ) (10 e) additional electron goes to 9 orbit making 9 2 Co. C 8 2 3 4 9 2 1 3 (X 2 i ) (11 e) additional electron goes to 1 orbit making 1 4 Co. N 8 2 3 4 9 2 1 4 (X 1Σ) (12 e)

Comparison of theoretical and expt. Result: *r 0 Parameter Theoretical Expt. Symmetry X 3 i X 3 3 re 1. 696 1. 701* e 757 731. 7

Hyperfine structure: linewidth larger than normal! Q(3) line has linewidth 0. 42 cm-1 . decreases Q(5) line has linewidth 0. 23 cm-1 . decreases Q(8) line has linewidth 0. 19 cm-1 Linewidth 8 5 3 The (2, 0) band of the [18. 3] 3 3 – X 3 3 transition of Co. B

Hyperfine structure Observations: Q(3) has linewidth 0. 42 cm-1 : : Q(8) line decreases to 0. 19 cm-1 case a coupling scheme Hyperfine structure in the = 3 - X 3 3 transition and = 2 - X 3 2 transition We ascribe the large hyperfine interaction to both the Co and B atoms Atom scheme. I In case a coupling (mag. dip. ) 59 Co 7/2 4. 627 11 B 3/2 3 2. 688 1. 800 10 B

Summary *First experimental observation of the Co. B molecule *Preliminary analysis of the rotational lines showed that these vibronic bands are with ' = 2 - " = 2 and ' = 3 - " = 3 transitions • The ground state of Co. B is X 3 3 *In addition, another 25 vibrational band were observed, . however, more work is needed to find relationship among them. 22