1. 62nd OSU International Symposium on Molecular Spectroscopy TA12 Laser Spectroscopy of Iridium Monoboride Jianjun Ye, H. F. Pang, A. M-Y. Wong, J. W-H. Leung, and A. S-C. Cheung Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. China 1

2. Introduction Some metal-containing boride molecules: *The spectroscopic studies of diatomic metal-containing borides are limited to the theoretical investigation. *Experimental investigation of this series of molecules remains almost unexplored. Only very few broide molecules: PdB, studied by electron spin resonance (ESR) spectroscopy. RhB, studied by laser induced fluorescence (LIF) spectroscopy. 2

3. Present work High resolution LIF spectrum of IrB between 545 to 610 nm has been recorded and analyzed: *(v, 0) with v = 0 – 3 of all four isotopic molecules: 191 Ir 10 B, 193 Ir 10 B, 191 Ir 11 B and 193 Ir 11 B were recorded. *Partially resolved hyperfine structure conformed to case a  coupling scheme has been observed. 3

4. Experimental Details The experimental setup of laser ablation/reaction and LIF 4

5. Molecule Production : Ir (Vapor) + B 2 H 6 → IrB + etc. Vaporization Laser : Nd:YAG, 10Hz, 532nm, 5mJ Free Jet Expansion : i) backing pressure: 5 atm (Ar + 1% B 2 H 6 ) ii) background pressure: 1x10 -5 Torr Spectral line width : about 250MHz 5

6. Results and Analysis Low-resolution LIF spectrum of  ' = 2 –  " = 3 band system of IrB 6 Wavenumber (cm -1 )

7. The (0,0) band of the  ' = 2 –  " = 3 transition of IrB 7 Wavenumber (cm -1 )

8. The (2,0) band of the  ' = 2 –  " = 3 transition of IrB 8 Wavenumber (cm -1 )

9. Molecular constants for the  ' = 2 and  " = 3 states of IrB (cm -1 ) 9 Parameter 191 Ir 11 B 193 Ir 11 B 191 Ir 10 B 193 Ir 10 B  ' = 2 T3T3 18350.286(2)18349.943(2) B0.47235(3)0.47204(3) T2T2 17791.129(2)17790.787(2) B0.47455(2)0.47424(3) T1T1 17186.970(2)17186.679(2) B0.47321(2)0.47294(2) T0T0 16541.845(1) 16535.824(2) B0.47336(4) 0.51860(2)  " = 3 T0T0 0.000 B0.51809(4) 0.56684

10. Reduced term value plot of v = 2 level of  = 2 and  = 3 states of IrB 10

11. Electronic configuration IrN 1  2 1  4 2  2 1  4 IrC 1  2 1  4 2  2 1  3 IrB 1  2 1  4 2  2 1  2 ?  2  1  +, 3  ¯ and 1  There is no  = 3 substate from  2 IrB 2p 6s 5d 33 22 11 11 22 11 Possible electronic configuration for the ground state of IrB (1) 1  2 1  4 2  2 1  1 2  1 1 , 3 , 1 , 3  (2) 1  2 1  4 2  2 2  21 , 3  Tentative assignment Ground state X 1  3 Excited state [ 16.5 ] 1  2

12. 12 The (1,0) band of the  ' = 2 –  " = 3 transition of IrB with partially resolved hyperfine structure Wavenumber (cm -1 )

13. Analysis of hyperfine structure Hyperfine structure in the [16.5] 1  2 - X 1  3 transition Judging from the size of the atomic magnetic moment for both AtomI  (mag. dip.) 193 Ir3/20.16 B3/22.688 We ascribe the large hyperfine interaction to the B atom In case a  coupling scheme

14. For a 1  3 state (  = 3 and  = 0) h" = 3a For a 1  2 state (  = 2 and  = 0) h' = 2a Hyperfine structure Q(3) line Case a  F = I + J 7/2 F J = 3 1212 X13X13 9/2 5/2 3/2 9/2 7/2 5/2 3/2 q(F”)

15. 15 The (1,0) band of the  ' = 2 –  " = 3 transition of IrB with partially resolved hyperfine structure Wavenumber (cm -1 )

16. Using linewidth measured from the Q and P branches. The hyperfine constants are estimated to be X 1  3 state h = 0.0286 cm -1 [16.5] 1  2 stateh = 0.0116 cm -1

17. for X 1  3 state for [16.5] 1  2 state

18. Summary 18 *Preliminary analysis of the rotational lines showed that these vibronic bands are with  ' = 2 and  " = 3. *Partially resolved hyperfine structure conformed to case a  coupling scheme has been observed.

19. Acknowledgments 19 This work was supported by grants from the Research Grants Council of the Hong Kong SAR, China (Project No. HKU 7015/04P) and Committee on Research and Conference Grants, The University of Hong Kong.