Spectral Line Parameters Including Temperature Dependences of N 2 - and Self-broadened Widths in the Region of the 9 band of C 2 H 6 using a Multispectrum Fitting technique V. Malathy Devi & D. Chris Benner, The College of William and Mary, Williamsburg, VA , USA. C.P. Rinsland & M.A.H. Smith, NASA Langley Research Center, Hampton, VA , USA. R.L. Sams & T.A. Blake, Pacific Northwest National laboratory, P.O.Box 999, MS K8-88, Richland, WA, 99352, USA. Jean-Marie Flaud, Laboratoire Interuniversitaire des Systems Atmospherque, CNRS, France. K. Sung & L.R. Brown, Jet propulsion Laboratory, California Institute of Technology, Pasadena, CA USA. A.W. Mantz, Connecticut College, New London, CT 06320, USA.

The 9 band near 822 cm -1 is observed in the composite unapodized CIRS spectrum (above) taken at medium resolution (1.7 cm -1 ) at mid-latitudes. [A. Coustenis et al. Icarus 2007;189: doi: /j.icarus ].

Comparison of a Spectrum of Titan to our Laboratory Spectrum Titan’s Atmospheric Spectrum showing the C 2 H 6 features. Courtesy of: Henry Roe, Lowell Observatory A laboratory spectrum recorded with the Bruker IFS 125HR FTS at JPL R Q(J, 2) Sub- band is shown in both figures.

r Q 0 sub-band. (a) Low pressure C 2 H 6 spectrum illustrating the high density of lines. (b) N 2 -broadened C 2 H 6 spectrum. Features of Individual J transitions are completely obscured. Multispectrum technique allows fitting such spectra to great advantage. Only two of the 43 spectra used in the analysis are shown here.

r Q 0 sub- band. A few spectra of C 2 H 6 +N 2 recorded at various temperatures, pressures, and paths are shown as examples.

Different sub- band series ( p Q, r P, p P) Effects of temperature and pressure on the relative strengths of these transitions

43 high resolution ( to cm -1 ) spectra at temperatures between 149 K and 298 K are fitted simultaneously. The set includes 17 pure and 26 lean mixtures of C 2 H 6 in N 2. Temperature (K) Gas MixtureC 2 H 6 Volume Mixing Ratio Path (m)Pressure Range (Torr) Number of Spectra 297.2C2H6C2H C2H6C2H to C 2 H 6 +N to C 2 H 6 +N to to C2H6C2H to C 2 H 6 +N 2 ~ to C2H6C2H to C 2 H 6 +N 2 ~ to C2H6C2H to C 2 H 6 +N 2 ~ to C2H6C2H to C 2 H 6 +N 2 ~ to C2H6C2H C 2 H 6 +N 2 ~

43 spectra fitted simultaneously. Tick marks at the top correspond to all transitions (>430) included in the fit. HB=HOT BAND ( ) No pressure- induced shifts, line mixing or speed dependence required to fit the spectra.

r Q 0 sub-band head. The top panel shows the fitted spectra and the bottom panel represents the weighted fit residuals on a magnified vertical scale. Overlap and blending of fundamental and hot-band transitions further complicates the analysis.

Well separated J,K transitions in this p P series vary from 7 to17(J″) and 1 to 6 (K″). The torsional split components overlap at high pressures. Hot-band transitions ( 9 +  -  ) are marked with (*). No pressure- induced shifts were required to fit even these well-separated lines.

Triangles and circles are measured widths from multispectrum fit. The stars correspond to widths that are calculated from constrained n by empirical linear fits: n= a+b  (J-c).

Measured N 2 - and Self-Widths vs. M (M=J′=J″ for Q sub- bands). Units of widths are cm -1 atm -1 at 296 K. LEFT: r Q bands RED: Self-Widths BLUE: N 2 -Widths RIGHT: p Q bands RED: Self-Widths BLUE: N 2 -Widths Ratio of Self- Widths to N 2 - Widths =1.40±0.05

Measured values of n from multispectrum fit.

Measured Temperature dependence exponents ( n ) of N 2 - and Self-Widths vs. M (M=J′=J″) in 17 Q sub-bands. LEFT: r Q Sub- bands RED: Self-Widths BLUE: N 2 -Widths RIGHT: r Q Sub- bands RED: Self-Widths BLUE: N 2 -Widths n for Self- Widths < n for N 2 -Widths

“Fitted” Temperature dependence exponents ( n ) for N 2 - and Self-Widths vs. M (M=J′=J″ for Q sub-bands). LEFT: r Q Sub-Bands RED: Self-Widths BLUE: N 2 -Widths RIGHT: p Q Sub- Bands RED: Self-Widths BLUE: N 2 -Widths n for self- Widths < n for N 2 -Widths

Measured N 2 - and Self-Widths vs. M (M=J′=J″ for all Q sub-bands). RED: Self-Widths BLUE: N 2 -Widths “Fitted” n using an empirical linear Equation: n= a + b  (J-c) BLUE: N 2 -Widths RED: Self-Widths Mean N 2 - to Self- Width = 1.40±0.05

(a)N 2 -Widths vs. K″ BLUE: p Q Sub-Bands RED: r Q Sub-Bands (b) Self-Widths vs. K” BLUE: p Q Sub-Bands RED: r Q Sub-Bands K″+0.05*(J″-K″) is used for pattern recognition Half-width coefficients are in Units of cm -1 atm -1 at 296 K

Values for a and b using n=a+b  (J-c), and the half-width coefficients for the highest J (=M=J″=J′ in Q sub-bands) for 9 measured r Q sub- bands. Sub-bandFor N 2 broadeningFor self broadening N 2 and self broadening abWidth at Jab c and J p Q(J,K=9)0.884(5)0.0076(11)0.998(17)0.592(6)0.0092(12)0.731(18)16, 31 p Q(J,K=8)0.799(5)0.0096(12)0.933(18)0.591(6)0.0109(13)0.744(19)16, 30 p Q(J,K=7)0.841(3)0.0131(7)1.02(12)0.647(5)0.0115(8)0.809(13)16, 30 p Q(J,K=6)0.878(3)0.0158(6)1.10(10)0.694(5)0.0172(7)0.936(11)16, 30 p Q(J,K=5)0.787(3)0.0131(5)1.06(1)0.579(4)0.0137(6)0.867(13)13, 34 p Q(J,K=4)0.821(2)0.0087(3)0.987(7)0.650(4)0.0079(5)0.800(9)13, 32 p Q(J,K=3)0.878(2)0.0162(4)1.18(7)0.792(3)0.0085(5)0.964(9)13, 32 p Q(J,K=2)0.781(2)0.0054(3)0.895(7)0.690(4)0.0041(4)0.775(9)13, 34 p Q(J,K=1)0.808(2)0.0123(3)1.04(6)0.706(3)0.0074(4)0.847(9)13, 32 The half-width coefficients are in units of cm -1 atm -1 at 296 K.

Comparison of Temperature Dependences ( n 2 ) of Self-Widths: This Study vs. Nguyen et al. (J. Mol. Spectrosc. 2008;39: ) a This study. The error bars for positions and temperature dependence exponents are twice the standard deviation. b Nguyen et al. Reported temperature dependence exponents were calculated from their measured self-broadened half-width coefficients at three different temperatures (242.2, and K). Line  (cm -1 ) a n 2 (This work) Voigt profile a n 2 Rautian profile b p Q(17,9) (1)0.602 ± ± p Q(16,9) (1)0.592 ± ± p Q(15,9) (1)0.583 ± ± p Q(13,5) (1)0.579 ± ± p Q(12,5) (1)0.566 ± ± p Q(11,5) (1)0.552 ± ± p Q(7,5) (1)0.497 ± ± p Q(6,5) (1)0.483 ± ± p Q(13,2) (1)0.690 ± ± p Q(12,2) (1)0.686 ± ± p Q(11,2) (1)0.682 ± ± 0.115

ACKNOWLEDGMENTS The experimental spectra for the present study were recorded at the W. R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy’s Office of Biological and Environmental Research located at Pacific Northwest National Laboratory (PNNL) and the Jet Propulsion Laboratory (JPL) in Pasadena, California. PNNL is operated for the United States Department of Energy by the Battelle Memorial Institute under Contract DE-AC05- 76RLO1830. NASA’s planetary atmospheres program supported the work performed at NASA Langley Research Center and the College of William and Mary. The research at the JPL and Connecticut College was performed under contracts and grants with NASA.