1. Continuous-Wave Cavity Ringdown Study of the 14 N 2 + Meinel System 2-1 Band and the First Positive Band System of N 2 * Departments of Chemistry and Astronomy, University of Illinois at Urbana-Champaign ŧ Department of Chemistry, University of Wisconsin-Madison Susanna L. Widicus Weaver Bogdan Negru Michael Wiczer Brian A. Tom Joshua P. DiGangi ŧ Benjamin J. McCall

2. The Meinel System of 14 N 2 + OSU MolSpec Abstract from 1951 IR Auroral Emission Bands of N 2 + observed by Meinel in 1950 Conference on Auroral Physics University of Western Ontario, 1951

3. The Meinel (A 2  u -X 2  g + ) System of N 2 + '' ' 0123456 09016684146992590513-1530-3540 1108898715657244632387343-1666 212733105588416630642302187177 31454612371102298120604340001990 41632914155120139903782757833774 518083159081376611656958075375527 6198061763115489133801130392607250 72150019325171831507312967109538944 823163209881884616737146601261710607 924797226222048018370162941425112241 1026400242262208319974178971585413845 1127974257992365721548194711742815418 1229518273432520123092210151897216962 1331032288582671524606225292048618477 Calculated Experimental Adapted from Tarsitano & Oka J. Mol. Spec. 219, 2003. 10200 – 10600 cm -1 diode laser Dalby and Douglas first characterized the N 2 + Meinel system in the laboratory in 1951 (Phys. Rev. 84).

4. The First Positive Group (B 3  g – A 3  g + ) of N 2 '' ' 0123456789 09512807966745297394726251332 1112179784837970025652433130371772535 21289411461100568678732960074713344822121004 314540131081170310326897676546361509638592681 4161601472713321119441059492737979671454774270 51774916316149111351312184108629668830370675859 619309178761647116093147421242211129986286277419 72084019407180021662516274139631266011395101588960 8209091950418126167771645514161128961167010462 92097619599182492692716612143691313211924 1021041196921831017076168111457513307 11211051987318489172241598814780 122116619873186071737016163 Calculated Experimental Adapted from Dieke & Heath Johns Hopkins Spec. Report 17, 1959 & Roux & Michaud J. Mol. Spec. 97, 253, 1983. First observed in the visible by Deslandres in 1902 (C. R. Society, Paris, 134) 10200 – 10600 cm -1 diode laser

5. The A 2  u -X 2  g + System of 14 N 2 + The A 2  u state displays -doubling and Hund’s case a applies. The X 2  g + state of N 2 + is split by spin-rotation interaction. Hund’s case b applies. P, Q, and R-type vibronic transitions are allowed. 2g+2g+ F1F1 F1F1 F1F1 F2F2 F2F2 F2F2 4 3 2 N 2.5 3.5 4.5 3.5 2.5 J 1.5 ---- ++++ ---- -+-+ +-+- -+-+ +-+- -+-+ -+-+ +-+- -+-+ +-+- +-+- 4.5 3.5 2.5 J 1.5 5.5 2.5 3.5 1.5 4.5 5.5 J 2  3/2 (F 1 ) 2  1/2 (F 2 ) R 21 R 22 Q 21 Q 22 P 21 P 22 R 11 R 12 Q 11 Q 12 P 11 P 12

6. The B 3  g – A 3  g + System of N 2 Hund’s case a applies for the B 3  u state at low J, and an intermediate between Hund’s cases a and b applies at high J. The 3  g state is split into 6 sub-states Hund’s case b applies for the A 3  g + state. P, Q, and R-type vibronic transitions are allowed. 3g+3g+ 3  0g 4 3 2 N J 1 0 354354 243243 132132 021021 0 F1F1 F3F3 F1F1 F2F2 F3F3 F1F1 F2F2 F3F3 F1F1 F2F2 F3F3 F1F1 F2F2 1 2 fefe N J 2 fefe N J 3 2 fefe Q 11 P 11 R 11 Q 12 P 12 R 12 Q 13 P 13 R 13 3  1g 3  2g Q 21 P 21 R 21 Q 22 P 22 R 22 Q 23 P 23 R 23 Q 31 P 31 R 31 Q 32 P 32 R 32 Q 33 P 33 R 33

7. CW Cavity Ringdown Spectroscopy (cw-CRDS) A high finesse cavity is placed around the discharge. Laser light is coupled into the cavity, which is cycled in and out of resonance. When the cavity is on resonance the laser light is diverted or switched off. The exponential decay rate is a direct measurement of absorption.

8. Experimental Setup

9. Spectral Calibration Mode Hop

10. The N 2 + Spectrum 0.03 cm -1  min = 2 x 10 -9 cm -1 3100 V, 70 mA N 2 /Ar discharge

11. N 2 * vs N 2 +

12. The A 2  u -X 2  g + System of 14 N 2 +

13. 14 N 2 + Line Assignments Frequencies calculated from Miller et al., J. Chem. Phys. 80, 1984 and Ferguson et al., J. Mol. Spec. 153, 1992. Intensities calculated from Earls, Phys. Rev. 48, 1935.

14. Spectral Parameters Determined for the 14 N 2 + 2-1 vibronic band TvTv 10558.1 10558.0931(25) BvBv 1.697391(67) 1.697442(87) DvDv 5.91(10) x 10 -6 5.952(75) x 10 -6 AvAv -74.6332(18) -74.6417(43) A dv -8.0(11) x 10 -5 -2.98(5) x 10 -5 qvqv -3.08(11) x 10 -4 -3.37(6) x 10 -4 pvpv 4.87(27) x 10 -3 5.18(19) x 10 -3 BvBv 1.903373(13)1.903499(88) DvDv 5.942(8) x 10 -6 5.997(75) x 10 -6  9.197(27) x 10 -3 9.31(54) x 10 -3 Lower State Upper State Fit RMS = 0.009 cm -1 for 95 lines † Ho et al., J. Mol. Spec. 153, 1992 Ferguson et al., J. Mol. Spec. 153, 1992 ParameterPrevious Studies † Our Work

15. The 14 N 2 * Problem Frequencies calculated from Dieke and Heath Johns Hopkins Spectroscopic Report 17, 1959. Intensities calculated from Budo, A. Z. fuer Phys. 105, 1937; Dieke and Heath Johns Hopkins Spectroscopic Report 17, 1959; Biloiu, Sun, Harvey, & Scime J. of App. Phys. 101, 2007.

16. Conclusions and Future Work The cw-CRDS spectra of N 2 + and N 2 * from 10227 - 10590 cm -1 have been acquired. 95 N 2 + lines from the 2-1 band of the Meinel system have been assigned and spectral parameters determined. More assignments are underway. ≥ 400 lines from the first positive band system of N 2 * have been identified. Final assignment and determination of spectral parameters is underway. Lines from the 3-2 band of the N 2 + Meinel system may be observable.

17. Acknowledgments Brian Tom NASA Laboratory Astrophysics The McCall Group http://astrochemistry.uiuc.edu Bogdan Negru Former group members Josh DiGangi, Brian Pohrte, and Matthew Zwier NSF CHE ACS Dreyfus UIUC Michael Wiczer Christopher G. Tarsitano for the N 2 + spectral fitting routine