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

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

The Meinel (A 2  u -X 2  g + ) System of N 2 + '' ' Calculated Experimental Adapted from Tarsitano & Oka J. Mol. Spec. 219, – cm -1 diode laser Dalby and Douglas first characterized the N 2 + Meinel system in the laboratory in 1951 (Phys. Rev. 84).

The First Positive Group (B 3  g – A 3  g + ) of N 2 '' ' Calculated Experimental Adapted from Dieke & Heath Johns Hopkins Spec. Report 17, 1959 & Roux & Michaud J. Mol. Spec. 97, 253, First observed in the visible by Deslandres in 1902 (C. R. Society, Paris, 134) – cm -1 diode laser

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 F2F N J J 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

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 N J 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

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.

Experimental Setup

Spectral Calibration Mode Hop

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

N 2 * vs N 2 +

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

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

Spectral Parameters Determined for the 14 N vibronic band TvTv (25) BvBv (67) (87) DvDv 5.91(10) x (75) x AvAv (18) (43) A dv -8.0(11) x (5) x qvqv -3.08(11) x (6) x pvpv 4.87(27) x (19) x BvBv (13) (88) DvDv 5.942(8) x (75) x  9.197(27) x (54) x Lower State Upper State Fit RMS = 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

The 14 N 2 * Problem Frequencies calculated from Dieke and Heath Johns Hopkins Spectroscopic Report 17, 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.

Conclusions and Future Work The cw-CRDS spectra of N 2 + and N 2 * from 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.

Acknowledgments Brian Tom NASA Laboratory Astrophysics The McCall Group 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