1. Fourier Transform Emission Spectroscopy of New Visible Systems of NbN R. S. Ram Department of Chemistry, University of Arizona, Tucson, AZ 85721 And P. F. Bernath Department of Chemistry, University of Waterloo, Waterloo, Ont. Canada N2L 3G1

2. Introduction Chemical importance Transition metal-containing molecules represent simple metal systems where d electrons take part in the bonding. Such molecules provide ideal models for understanding the bonding and reactivity in transition metal systems. Recent interest in these molecules can also be attributed to their importance in catalysis. Niobium 93 Nb has a large magnetic moment (6.1435 nuclear magnetons) and a large nuclear spin (9/2) that produces impressive hyperfine splittings in the spectra of NbO and NbN. Their spectra, therefore, provide valuable information about the electronic structure and bonding in these molecules. Astrophysical importance Transition metal atoms have relatively large abundances in many stars. Like their diatomic oxides and hydrides, there is a possibility that nitride molecules may also be found in the atmospheres of cool stars. If found, their spectra will provide data on the abundance of nitrogen in cool stars.

3. Previous work First Observation of a 3 Φ-X 3 Δ transition. [T. M. Dunn and M. K. Rao, Nature 222, 266 (1969)] Rotational analysis of the 3 Φ-X 3 Δ transition. [J.-L. Fémenias, C. Athénour and T. M. Dunn, JCP 63, 2861 (1975)] Laser spectroscopy: X 3 Δ, a 1 Δ, A 3 Σ -, b 1 Σ +, B 3 Φ, C 3 Π, e 1 Π, and f 1 Φ states. X 3 Δ 2 -X 3 Δ 1 = 400.5 ± 1 cm -1 X 3 Δ 3 -X 3 Δ 2 = 490.5 ± 1 cm -1 [Azuma, Merer and coworkers JCP 91, 1 (1989)] [Azuma, Merer and coworkers JCP 100, 4133 (1994)] Ab initio predictions of spectroscopic properties of NbN. [Langhoff and Bauschlicher, JMS 143, 169 (1990)] FT observation of the near infrared transitions of NbN. f 1 Φ-c 1 Γ, e 1 Π-a 1 Δ, C 3 Π 0+ -A 3 Σ 1 -, C 3 Π 0- -A 3 Σ 1 -, C 3 Π 1 -a 1 Δ, C 3 Π 1 -A 3 Σ 0 -, d 1 Σ + -A 3 Σ 0 -, d 1 Σ + -b 1 Σ +. [R.S. Ram and P. F. Bernath, JMS 201, 267 (2000)]

4. Langhoff and Bauschlicher, JMS 143, 169 (1990)

5. Azuma, Merer and coworkers, JCP 100, 4138 (1994)

6. Ram and Bernath, JMS 201, 267 (2000) New states New state 4dδ 1 4dσ 1 ? 5sσ 1 4dπ 1 ?

7. Experimental Microwave discharge of NbCl 5 vapor mixed with 1.9 Torr of He Fourier transform spectrometer of the National Solar Observatory at Kitt Peak 8000-20000 cm -1 :17500-35000 cm -1 : UV beam splitter Super blue Si Filter: OG530 Filter: CuSO 4 Resolution: 0.02 cm -1 Resolution: 0.03 cm -1 Scans: 6 (27 minutes)Scans: 1 (7 minutes)

8. Present work Fourier transform emission spectroscopy of new transitions: 3 Π 0± - 3 Δ 1 (18500-19800 cm -1 ):0-0, 0-1 3 Π 1 - 3 Δ 2 (18500-19800 cm -1 ):0-0, 0-1 3 Π 2 - 3 Δ 3 (18500-19800 cm -1 ):0-0, 0-1 ΔΩ=0 (Ω"=2) (24000-25415 cm -1 ): 0-0, 1-1, 0-1 ΔΩ=0 (Ω"=1) (25519 cm -1 ): 0-0 ΔΩ=0 (Ω"=1) (25535 cm -1 ): 0-0

9. A compressed portion of the 3 Π-X 3 Δ transition of NbN

10. The 3 Π 2 -X 3 Δ 3, 0-0 band of NbN

11. New NbN bands in the 25000-26000 cm -1 region

12. A portion of the ΔΩ=0 [Ω"=X 3 Δ 2 ], 0-0 band of NbN

13. Constants (in cm -1 ) for the observed states of NbN

14. Summary The following new transitions of NbN have been observed in the 18500-26000 cm -1 region using Fourier transform emission spectroscopy. 3 Π-X 3 Δ (18500-19800 cm -1 ):0-0, 0-1 ΔΩ=0 (Ω"=2) (24000-25415 cm -1 ): 0-0, 1-1, 0-1 ΔΩ=0 (Ω"=1) (25519 cm -1 ): 0-0 ΔΩ=0 (Ω"=1) (25535 cm -1 ): 0-0 A rotational analysis of these bands provide spectroscopic constants for the new states. Most of the excited states are perturbed by unknown electronic states. No theoretical predictions are available for these states.

15. Acknowledgments NASA laboratory astrophysics program National Solar Observatory Mike Dulick