Fourier Transform Emission Spectroscopy of Some New Bands of ReN

R. S. RamDepartment of Chemistry, University of Arizona,

Tucson, AZ 85721

and

P. F. BernathDepartment of Chemistry, University of York,

Heslington, York, UK YO10 5DD

IntroductionChemical importance

• Transition metal-containing diatomics represent simple metal systems where d

electrons participate in the bonding. These molecules provide models for understanding the bonding and reactivity in transition metal systems. Recent interest in transition metal nitrides are in part due to their importance in catalysis.

• Experimental observations test the predictions of ab initio calculations.

Astrophysical importance

Transition metal atoms and nitrogen have relatively large abundances in many stars. If found, the spectra of transition metal nitrides would provide data on the abundance of nitrogen in cool stars.

Previous work • First observation of a [=1] – X0+ transition at 23746 cm-1.

[R.S. Ram, P.F. Bernath, W.J. Balfour, J. Cao, C.X.W. Qian and S.J. Rixon, JMS 168, 350 (1994)]

• LIF observation of visible spectrum of ReN in the 375-542 nm region. [W.J. Balfour, J. Cao, C.X.W. Qian and S. J. Rixon, JMS 183, 113(1997)]Several transitions were observed by laser excitation spectroscopy.Ground state was assigned as X3- (0+) labeled as X0+.Possible configurations of low-lying electronic states discussed.

• LIF and dispersed fluorescence study of ReN.[J. Cao, W.J. Balfour and C.X.W. Qian, JPC 101, 6741 (1997)]Deperturbation analysis of the [=1] - X0+ system at 18513 cm-1.Tentative location of the low-lying 3-

1, 33, 32, 31 and 1+ states from dispersed fluorescence.

Periodic Table

Re is in group 7, like Mn, and ReN is isoelectronic with WO (Hund’s case a′ X3Σ- ground state).

Balfour and co-workers

12 valence electrons

ReN: 1δ2 3σ2 g. s. configuration; X3Σ- term for Hund’s case (a), and X0+ and A1 for case (a′).

Formal triple bond for ReN, but no ab initio calculations are available.

Balfour and co-workers

Experimental

• Rhenium hollow cathode discharge with 3.0 Torr of Ne and 5 mTorr N2

300 V, 457 mA current

• Spectra observed with the Fourier transform spectrometer of the

National

Solar Observatory at Kitt Peak

10000-19500 cm-1 17000-29000 cm-1

UV beam splitter UV beam splitter

Si diode detectors Si diode detectors

Filter: RG495 Filter: CuSO4

Resolution: 0.02 cm-1 Resolution: 0.02 cm-1

Scans: 6 (60 minutes) Scans: 8 (60 minutes)

The following two new ReN bands have been identified in the visible region:

0+ – A1 22110 cm-1

0- – A1 22224 cm-1

Observed by Balfour et al. [JMS 183, 113 (1997)]

Present observations

A compressed portion of the new visible bands of ReN

A portion of the 0+ - A1, 0-0 band of ReN at 22110 cm-1

Constants (in cm-1) for the observed states of ReN

Constants A1 0+ 0-

Tv 2616.283(11) 24726.108(11) 24840.636(12)

Bv 0.480886(15) 0.461685(15) 0.460406(15)

107 × Dv 3.384(21) 4.281(25) 3.787(22)

104 × qv 2.4700(39) -- --

Numbers in parentheses are one standard deviation in the last digits

Present term value for the A1 state Value from Balfour et al. (1997)

2616.283 (11) cm-1 2630 (100) cm-1

Summary

• Two new ReN bands having a common lower state have been observed in the 21000 -22500 cm-1 region using Fourier transform emission spectroscopy.

0+ - A1 (0-0) 22110 cm-1 0- - A1 (0-0) 22224 cm-1

The upper state of the 0+ state at 22110 cm-1 is common to the upper state of the [24.7]0+ state [Balfour et al. (1997)], which places the A1 state at 2616.283 cm-1.

• A rotational analysis of these bands provide spectroscopic constants for the new states.

• No theoretical predictions are available for these states.

Acknowledgments

NASA laboratory astrophysics program

Walter Balfour

NSERC, Canada

National Solar Observatory

Mike Dulick