63 rd OSU International Symposium on Molecular Spectroscopy

63 rd OSU International Symposium on Molecular Spectroscopy Laser Spectroscopy of Iridium Compounds H. F. Pang, Jianjun Ye, J. W-H. Leung, G. H. Chen and A. S-C. Cheung Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. China 1

Outline • Introduction • Experimental work – Ir. N & Ir. C • Theoretical calculations – Ir. B • Results and discussion 2

Introduction Why iridium-containing compounds? Ø Many Ir compounds are good catalysts for hydrogenation of alkenes and alkynes, reduction of nitrogenous function groups etc. Ø The spectroscopic studies of diatomic iridium-containing compounds are limited. Ø Comparison of Ir compounds (Ir. B, Ir. C, Ir. N and Ir. O) shows a systematic trend. 3

Present work 1. Experimental work - High resolution LIF spectrum of Ir. C and Ir. N between 390 and 520 nm has been recorded analyzed. 2. Theoretical calculations on Ir. B has been performed. 4

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Molecule Production: Ir (Vapor) + CH 4 → Ir. C + etc. Ir (Vapor) + NH 3 → Ir. N + etc. Vaporization Laser: Nd: YAG, 10 Hz, 532 nm, 5 m. J Free Jet Expansion: i) backing pressure: 5 atm. (Ar + 3% CH 4 or NH 3 ) ii) background pressure: 1 x 10 -5 Torr Spectral line width: about 0. 05 cm-1 6

Ir. C Authors (years) Report Jansson et al (1970) Grating Spectrograph (emission) 660 – 850 nm E 2Δ 5/2 – X 2Δ 5/2 system E 2Δ 3/2 – X 2Δ 3/2 system D 2Φ 7/2 – X 2Δ 5/2 system Marr et al (1996) LIF Spectroscopy 578 – 530 nm Fine, hyperfine constants and permanent electric dipole moment of D 2Φ 7/2 – X 2Δ 5/2 system Tan et al (1997) Ab initio calculation Confirm the X 2Δ 5/2 theoretically and reassigned the E & D system T. Ma et al (2004) Cavity Ring down Spectroscopy 445 - 500 nm L 2Φ 7/2 – X 2Δ 5/2 system 7

Low-resolution LIF spectrum of new band system of Ir. C K 2Π 3/2 (2, 0) L 2Φ 7/2 - Χ 2Δ 5/2 (2, 1) L 2Φ 7/2 - Χ 2Δ 5/2 (0, 0) 8

New band of 2Π 3/2 - X 2Δ 5/2 transition of Ir. C 9

K 2Π 3/2 - X 2Δ 5/2 transition of Ir. C 10

Molecular constants for the new states of Ir. C (cm-1) K 2Π 3/2 Band Parameter 191 Ir. C 193 Ir. C (2, 0) T B 20887. 19 0. 49481 20886. 63 0. 49444 (1, 0) T B 20069. 88 0. 49809 20069. 56 0. 49767 (0, 0) T B 19236. 16 0. 50303 19236. 12 0. 50275 [22. 3] 2Π 3/2 Band Parameter (0, 0) T B 191 Ir. C 193 Ir. C 22304. 402 0. 46490 11

Molecular constants for other new vibonic states of Ir. C (cm-1) State Parameter 191 Ir. C 193 Ir. C T B 25364. 373 0. 46403 25363. 582 0. 46200 2 3/2 T B 24596. 951 0. 46603 24596. 391 0. 46503 2 3/2 T B 24312. 807 0. 46671 24312. 232 0. 466567 2 3/2 T B 23936. 724 0. 47021 23936. 286 0. 46977 2 3/2 T B 23809. 408 0. 47563 23809. 111 0. 47316 12

Ir. C Electronic configuration Ground state: 1 2 1 4 2 2 1 3 X 2 5/2 Excited state: 1 2 1 4 2 2 1 (2)2 , 4 , 2 H 1 2 1 4 2 1 1 3 2 1 (2)2 , 4 , (2)2 , 4 These excited electronic configurations can give rise to four 2 states. 13

Ir. N Authors (years) Report Marr et al (1996) LIF Spectroscopy – Optical Stark 531 – 696 nm A 1 – X 1 S+ system - fine, hyperfine & permanent dipole moment Ram et al (1997) FT Spectroscopy A’ 1 –X 1 S+ system A 1 – X 1 S+ system Steimle et al (1996) LIF Spectroscopy – Optical Zeeman Spectroscopy A 1 – X 1 S+ system g. J factor Ram et al (1999) FTS and ab initio calculations A” 1 S+ – X 1 S system a 3 – X 1 S system 14

Low-resolution LIF spectrum of new band system of Ir. N 15

New band of 1Σ+ - X 1Σ+ transition of Ir. N 16

Molecular constants for the new 1 + state of Ir. N (cm-1) State Parameter 191 Ir. N 193 Ir. N 1 S+ T 25 137. 927 25 137. 75 B 0. 437 47 0. 435 21 T 24 024. 731 24 025. 090 B 0. 440 19 0. 438 83 T 0 0 0 B 0. 499 34* 0. 498 48* 1 S+ * Values taken from T. C. Steimle, J. Chem. Phys. 104(21), 1996. 17

Ir. N Electronic configuration Ground state: 1 2 1 4 2 2 1 4 X 1 Σ + Excited state: 1 2 1 4 2 1 1 4 3 1 1Σ+ , 3Σ+ 1 2 1 3 2 2 1 4 2 1 1Σ+ , 1Σ- , 3Σ+ , 3Σ- , 1 , 3 i These excited electronic configurations can give rise to a few 1Σ states. 18

Results and Analysis Low-resolution LIF spectrum of ' = 2 – " = 3 band system of Ir. B 19

Last year: Observed transition of Ir. B using LIF was assigned as [16. 5] 3Π 2 – X 3 3 Bond length determined: X 3 3 [16. 5] 3Π 2 r 0 = 1. 7675 Å re = 1. 8487 Å Possible electronic configuration for the ground state of Ir. B (1) (2) 1 2 1 4 2 1 1 3 1 2 1 4 1 3 2 1 1 , 3 i 1 , 3 , 1 , 3 20

Theoretical Study of the Ir. B molecule Computational method: MOLCAS - 6. 4 version Low-lying electronic states of iridium boride (Ir. B) have been investigated using the complete active space self-consistent field calculation followed by complete active space second-order perturbation theory (CASPT 2) (ie CASSCF-CASPT 2 level) Atom natural orbital basis sets Ir 24 s 21 p 15 d 11 f 4 g 2 h / 9 s 8 p 6 d 4 f 3 g B 14 s 9 p 5 d 3 f 2 g / 5 s 4 p 3 d 2 f The active space used in the CASSCF calculations comprised 5 d, 6 s orbitals of Ir and 2 s, 2 p orbitals of B. The calculations were performed in C 2 symmetry, so that the degenerate pairs of electronic states could be averaged. 21

Calculation results: States 1Δ 1 ∑+ 1 ∑ 1 П 1 П(II) 1 П(III) 3Δ 3 ∑+ 3Δ(II) 3 П 3 П(II) 3 П(III) 5Δ 5Δ(II) 5 ∑+ 5 П(III) Re(Å) CASPT 2 1. 7422 1. 7467 1. 8214 1. 8846 1. 7776 1. 8349 1. 7708 1. 7796 1. 8694 1. 8591 1. 9622 1. 9519 1. 9862 1. 9626 1. 9359 1. 8475 Te (cm-1) CASPT 2 2102. 86 2594. 06 13930. 21 14775. 20 16572. 67 20548. 54 0. 00 8242. 42 10912. 82 14524. 95 17438. 22 18483. 13 26088. 37 29244. 62 32902. 00 24583. 03 22

Ir. B X 3 3 [16. 5] 3Π 2 r 0 = 1. 7675 Å re = 1. 8487 Å 1. 7708 Å 1. 9622 Å Electronic configuration for the electronic states of Ir. B from ab initio calculations (observed transition: (e – is promoted form the 1 to the 1 ) (1)1 2 1 4 2 1 1 3 X 3 i (1)1 2 1 3 2 1 1 4 1 , 3 i 1 2 1 4 1 3 2 1 1 , 3 , 1 , 3 23

Electronic configuration 3 2 5 d 1 2 6 s 1 2 p 1 Ir B, C, & N 1 is a non-bonding orbital 2 is a slight anti-bonding orbital 24

Electronic configuration Ir. B 1 2 1 4 2 1 1 3 X 3 2 Ir. C 1 2 1 4 2 2 1 3 X 2 5/2 Ir. N 1 2 1 4 2 2 1 4 X 1 S + Ir. O 1 2 1 4 2 1 X 2 1/2 25

193 Ir. B 193 Ir. C 193 Ir. N L 2 7/2 ( 2 1 1 3 ) re = 1. 7557 Å we = 833. 3 wexe = 8. 01 Te = 20930. 45 [16. 5] 3 2 (2 1 1 3 1 4) ( ) re = 1. 8487Å we = 686. 96 wexe = 21. 06 To = 16203. 627 K 2 (2 2 1) ro = 1. 7229 Å To = 19248 G 1/2 = 832 A 1 (2 2 1 3 2 1) re = 1. 6847 Å we = 936. 73 wexe = 11. 65 To = 15186. 75 Excited state Ground state X 3 2 (2 1 1 3) ro = 1. 7675 Å D 2Φ 7/2 (2 2 1) ro = 1. 7216 Å To = 15277. 5 G 1/2 = 924 A’ 1 (2 1 1 4 2 1) re = 1. 6786 Å we = 1014. 06 wexe = 6. 62 To = 13135. 39 E 2 5/2 ro = 1. 7085 Å To = 15100. 81 G 1/2 = 953 a 3 (2 1 1 4 2 1) ro = 1. 6603 Å A = - 340. 53 To = 8840. 32 G 1/2 = 984. 36 X 2 5/2 (2 2 1 3) ro = 1. 6852 Å X 1 S+ (2 2 1 4) ro = 1. 6068 Å 26

Summary 27

Acknowledgments This work was supported by grants from the Research Grants Council of the Hong Kong SAR, China (Project No. HKU 7015/04 P) and Committee on Research and Conference Grants, The University of Hong Kong. 28