Infrared Spectra of N 2 -broadened 13 CH 4 at Titan Atmospheric Temperatures Mary Ann H. Smith 1, Keeyoon Sung 2, Linda R. Brown 2, Timothy J. Crawford 2, Arlan W. Mantz 3, V. Malathy Devi 4, and D. Chris Benner 4 1 Science Directorate, NASA Langley Research Center, Hampton, VA 23681, U.S.A. 2 Science Division, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, U.S.A. 3 Dept. of Physics, Astronomy and Geophysics, Connecticut College, New London, CT 06320, U.S.A. 4 The College of William and Mary, Williamsburg, VA 23187, U.S.A. MJ02-OSU 65th International Symposium on Molecular Spectroscopy, June 21-25, 2010

13 CH 4 spectra broadened by N 2  Pure sample spectrum at K 99% 13 C Pressure = 1.05 Torr Jmax ≈ 16  Sample + N 2 at K 13 CH 4 Pressure = 1.03 Torr P total = Torr Jmax ≈  Sample + N 2 at 79.5 K 13 CH 4 Pressure = 1.20 Torr P total = Torr Jmax ≈ MJ02-OSU 65th International Symposium on Molecular Spectroscopy, June 21-25, 2010

A closer look at low-T spectra I. MJ02-OSU 65th International Symposium on Molecular Spectroscopy, June 21-25, 2010

A closer look at low-T spectra II. MJ02-OSU 65th International Symposium on Molecular Spectroscopy, June 21-25, 2010

First retrievals: 13 CH 4 R(2) manifold  Why choose the R(2) manifold? Two lines only, well isolated at low P Low J lines are persistent at low T. No line mixing is expected between F and E symmetry species.  Selected 9 low-abundance spectra to allow self-broadening parameters to be fixed to literature values.  Retrievals for three T ranges Subset#1: 181 – 296 K Subset#2: 80 – 181 K Entire Set: 80 – 296 K  Retrievals at individual temperatures (296, 255, 225, 181, 129, and 79.5 K) to examine power-law T-dependence. MJ02-OSU 65th International Symposium on Molecular Spectroscopy, June 21-25, 2010

13 CH 4 R(2) Multispectrum Fitting Residuals Fitting residuals from the Entire set(►) from Subset #1 (▼) MJ02-OSU 65th International Symposium on Molecular Spectroscopy, June 21-25, 2010

Temperature Dependences γ o (T) = γ o (T o ) × (T o /T) n γ o (T) = half width at T at 1 atm T o = reference T (296 K unless otherwise noted) n = temperature dependence (Empirical power law) δ o (T) = δ o (T o ) + δ'×(T-T o ) δ o (T) = half width at T at 1 atm T o = reference T (296 K unless otherwise noted) δ' = temperature dependence Note that we do not use a power law here.  Lorentz line widths  Pressure-induced line shifts MJ02-OSU 65th International Symposium on Molecular Spectroscopy, June 21-25, 2010

Transitionγ0γ0 nδ0δ0 δ′ No. Spectra R2 F2 1 ( cm-1) Subset#1: 181 – 296 K (1)0.855(6)−0.0017(1)3(2)E-065 Subset#2: 80 – 181 K (3)0.898(5)−0.0012(6)7(4)E-065 Entire Set: 80 – 296 K (1)0.887(3)−0.0017(1)7(1)E-069 R2 E 1 ( cm-1) Subset#1: 181 – 296 K (1)0.801(7)−0.0019(1)1.3(2)E-055 Subset#2: 80 – 181 K (3)0.890(7) (7)4.3(5)E-055 Entire Set: 80 – 296 K (1)0.860(4)−0.0013(2)2.3(2)E (7) R(2) Preliminary Fit Results Note: Units of γ and δ are cm -1 atm -1 at 296K, units of δ′ are cm -1 atm -1 K -1, and n is unitless. MJ02-OSU 65th International Symposium on Molecular Spectroscopy, June 21-25, 2010

Evidence for departure from power law 13 CH 4 /N 2 fit to the power law, Sung et al., JMS in press (2010). 80K to 296K γ o (T) = γ o (T o ) × (T o /T) n Extra term proposed by Mondelain et al. for 12 CH 4 /N 2 (JMS, 2007) and 13 CO/He (15K to 300 K), 13 CO/Ar (APB, 2008) ln(γ o T ) = ln(γ o To ) +n 1 ln(T o /T) + n 2 ln 2 (T o /T) n 2 is the non-linear term (smaller that n 1 by a factor of 12) MJ02-OSU 65th International Symposium on Molecular Spectroscopy, June 21-25, 2010

13 CH 4 R(2) Results Comparison  HITRAN values are based on measurements from 210 K to room temperature; we measured widths and shifts from 80 K to 296 K.  Widths are about 3x greater at 80 K than at 296 K. Extrapolation using HITRAN08 parameters results in 6 to 10% underestimate of the 80 K line width.  The frequency shift for the E line is smaller than that for the F line at room temperature, but the different temperature dependences result in a 2x greater E line shift at 80 K.  Titan atmospheric p, T are ~93 K and 1.5 bar at surface, ~71 K and 128 mbar at tropopause. MJ02-OSU 65th International Symposium on Molecular Spectroscopy, June 21-25, 2010

R(2) Comparison with Other Results MJ02-OSU 65th International Symposium on Molecular Spectroscopy, June 21-25, 2010 SourceBroadenerT range (K)WidthWidth TdepShiftShift Tdep 13 CH 4 R2 F2 1 ( cm −1 ) HITRAN08 [38]air210 to − Smith et al. [43]air (5)− (6) Malathy Devi et al. [44]air (1)−0.0021(2) Present WorkN2N2 80 to (12)0.8874(27)− (13)0.7(1)E CH 4 R2 F2 1 ( cm −1 ) HITRAN08 [38]air − Smith et al. [42]air210 to (4)0.840(4)− (4)0.4(1)E-05 Smith et al. [45]N2N2 211 to (22)0.842(14)− (17)1.0(2)E CH 4 R2 E 1 ( cm −1 ) HITRAN08 [38]air210 to − Smith et al. [43]air (6)− (6) Malathy Devi et al. [44]air (2)−0.0024(2) Present WorkN2N2 80 to (13)0.8603(36)− (15)2.2(2)E CH 4 R2 E 1 ( cm −1 ) HITRAN08 [38]air − Smith et al. [42]air210 to (1)0.800(4)− (4)1.6(1)E-05 Smith et al. [45]N2N2 211 to (21)0.855(15)− (17)1.7(2)E-05 Table and references are from the paper by Sung et al., J. Mol. Spectrosc., in press (2010). Note: Units of Width and Shift are cm -1 atm -1 at 296K, units of Shift Tdep are cm -1 atm -1 K -1, and Width Tdep is unitless. Values in parentheses are 1σ statistical errors in units of the last digit quoted.

Fitting other R manifolds Fitting residuals (upper) and observed spectra (lower) for R(1)▼ MJ02-OSU 65th International Symposium on Molecular Spectroscopy, June 21-25, 2010 Results vs. T for R(0) and R(1)

R(0) and R(1) Comparison with Other Results MJ02-OSU 65th International Symposium on Molecular Spectroscopy, June 21-25, 2010 SourceBroadenerT range (K)WidthWidth TdepShiftShift Tdep 13 CH 4 R0 A1 1 ( cm −1 ) HITRAN08 [38]air210 to − Smith et al. [43]air (1)− (6) Malathy Devi et al. [44]air (1)−0.0032(3) Present WorkN2N2 80 to (1)0.679(3)−0.0013(1)5.2(1)E CH 4 R0 A1 1 ( cm −1 ) HITRAN08 [38]air210 to − Smith et al. [42]air210 to (0)0.70(0)−0.0027(0)1.6(0)E-05 Smith et al. [45]N2N2 211 to (11)0.709(8)− (11)2.26(14)E-05 Lepere et al. (2002)N2N2 188 to / CH 4 R1 F1 1 ( cm −1 ) HITRAN08 [38]air210 to − Smith et al. [43]air (0)− (4) Malathy Devi et al. [44]air (1)−0.0017(2) Present WorkN2N2 80 to (1)0.869(2)−0.0006(1)2.3(1)E CH 4 R1 F1 1 ( cm −1 ) HITRAN08 [38]air210 to − Smith et al. [42]air210 to (0)0.82(0)−0.0014(0)1.2(0)E-05 Smith et al. [45]N2N2 211 to (10)0.825(7)− (10)1.43(13)E-05 Reference numbers are from the paper by Sung et al., J. Mol. Spectrosc., in press (2010). Note: Units of Width and Shift are cm -1 atm -1 at 296K, units of Shift Tdep are cm -1 atm -1 K -1, and Width Tdep is unitless. Values in parentheses are 1σ statistical errors in units of the last digit quoted.

R(0) – R(3) Fit Results, 80 – 296 K Preliminary, work in progress Transitionγ0γ0 nδ0δ0 δ′ No. Spectra R0 A1 1 ( cm -1 ) (1)0.679(3)−0.0013(1)+5.2(1)E-059 R1 F1 1 ( cm -1 ) (1)0.869(2)−0.0006(1)+2.3(1)E-059 R2 F2 1 ( cm -1 ) (1)0.887(3)−0.0017(1)+7(1)E-069 R2 E 1 ( cm -1 ) (1)0.860(4)−0.0013(2)+2.3(2)E-059 R3 A2 1 ( cm -1 ) (1)0.773(4)−0.0011(1)+1.6(1)E (1)0.787(4)−0.0013(1)+1.0(2)E-059* R3 F2 1 ( cm -1 ) (2)0.805(6) (2)−1(3)E (2)0.828(5)−0.0044(2)−2.1(3)E-059* R3 F1 1 ( cm -1 ) (2)0.782(5)−0.0040(2)+7.1(2)E (2)0.842(2) (2)+5.3(2)E-059* Note: Units of γ and δ are cm -1 atm -1 at 296K, units of δ′ are cm -1 atm -1 K -1, and n is unitless. *Retrieved with line mixing. MJ02-OSU 65th International Symposium on Molecular Spectroscopy, June 21-25, 2010

Summary and Future Work Measured and observed Line widths and pressure-induced shifts for 13 CH 4 /N 2 R(0) – R(3) manifolds Temperature dependences in 80 – 296 K range Non-linearity in the T-dependence of the widths Continuing analysis of other 13 CH 4 manifolds Results to date agree with other measurements of 13 CH 4 and 12 CH 4 broadened by N 2 or by air. Line mixing and speed-dependence are considered. Self-broadening and self-shifts must be better quantified over the 80 – 296 K range to obtain accurate results for N 2 -broadening and shifts. MJ02-OSU 65th International Symposium on Molecular Spectroscopy, June 21-25, 2010

The Team and Acknowledgements Acknowledgements Research described in this talk was performed at Connecticut College, the College of William and Mary, NASA Langley Research Center and the Jet Propulsion Laboratory, California Institute of Technology, under contracts and cooperative agreements with the National Aeronautics and Space Administration. Malathy Keeyoon Linda Tim Arlan Mary Ann Chris MJ02-OSU 65th International Symposium on Molecular Spectroscopy, June 21-25, 2010