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

Infrared Spectra of N2-broadened 13CH4

at Titan Atmospheric Temperatures

Mary Ann H. Smith1, Keeyoon Sung2, Linda R. Brown2, Timothy J. Crawford2, Arlan W. Mantz3, V. Malathy Devi4, and D. Chris Benner4

1Science Directorate, NASA Langley Research Center, Hampton, VA 23681, U.S.A.2Science Division, Jet Propulsion Laboratory, California Institute of Technology,

Pasadena, CA 91109, U.S.A. 3Dept. of Physics, Astronomy and Geophysics, Connecticut College,

New London, CT 06320, U.S.A. 4The College of William and Mary, Williamsburg, VA 23187, U.S.A.

MJ02-OSU 65th International Symposium on Molecular Spectroscopy, June 21-25, 2010

13CH4 spectra broadened by N2

Pure sample spectrum at 295.8 K 99% 13C Pressure = 1.05 Torr Jmax ≈ 16

Sample + N2 at 295.8 K 13CH4 Pressure = 1.03 Torr Ptotal = 795.6 Torr Jmax ≈ 12 - 13

Sample + N2 at 79.5 K 13CH4 Pressure = 1.20 Torr Ptotal = 299.3 Torr Jmax ≈ 8 - 9


A closer look at low-T spectra I.


A closer look at low-T spectra II.


First retrievals: 13CH4 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 rangesSubset#1: 181 – 296 KSubset#2: 80 – 181 KEntire 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

13CH4 R(2) Multispectrum Fitting Residuals

Fitting residuals from the Entire set(►)from Subset #1 (▼)


Temperature Dependences

γo(T) = γo(To) × (To/T)n

γo(T) = half width at T at 1 atmTo = reference T (296 K unless otherwise noted)n = temperature dependence(Empirical power law)

δo(T) = δo(To) + δ'×(T-To)

δo(T) = half width at T at 1 atmTo = reference T (296 K unless otherwise noted)δ' = temperature dependenceNote that we do not use a power law here.

Lorentz line widths

Pressure-induced line shifts


Transition γ0 n δ0 δ′ No. Spectra

R2 F2 1 (1313.722 cm-1)

Subset#1: 181 – 296 K 0.0627(1) 0.855(6) −0.0017(1) 3(2)E-06 5Subset#2: 80 – 181 K 0.0609(3) 0.898(5) −0.0012(6) 7(4)E-06 5Entire Set: 80 – 296 K 0.0619(1) 0.887(3) −0.0017(1) 7(1)E-06 9R2 E 1 (1313.788 cm-1)

Subset#1: 181 – 296 K 0.0538(1) 0.801(7) −0.0019(1) 1.3(2)E-05 5Subset#2: 80 – 181 K 0.0516(3) 0.890(7) +0.0019(7) 4.3(5)E-05 5Entire Set: 80 – 296 K 0.0531(1) 0.860(4) −0.0013(2) 2.3(2)E-05 9

+0.0019(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.


Evidence for departure from power law

0 0.1 0.2 0.3 0.4 0.5 0.6

-1.3

-1.2

-1.1

-1

-0.9

-0.8

-0.7 13CH4(4)/N2R(2) F2 1 (1313.722 cm-1)R(2) E 1 (1313.788 cm -1)

log(To/T)

log

o

310 276 246 219 196 174 155 138 123 110 98 87 78T (K)

13CH4/N2 fit to the power law, Sung et al., JMS in press (2010). 80K to 296K

γo(T) = γo(To) × (To/T)n

Extra term proposed by Mondelain et al. for 12CH4/N2 (JMS, 2007) and 13CO/He (15K to 300 K), 13CO/Ar (APB, 2008) ln(γo

T) = ln(γoTo) +n1 ln(To/T) + n2 ln2(To/T)

n2 is the non-linear term (smaller that n1 by a factor of 12)


13CH4 R(2) Results Comparison

100 150 200 250 3000.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

Temperature (K)

half

wid

th c

oeffi

cien

t, o

(cm

-1/a

tm)

13CH4 (4) by N2: line broadening

R(2) F2

R(2) E

o(T) = o(To) x (To/T)n

oN

2

: This Worko

air, HITRAN 2008

oair

: Smith et a l.(2010)o

air: Devi et a l.(1988)

100 150 200 250 300-10

-8

-6

-4

-2

0

2

Temperature (K)Fr

eq. s

hift

coef

ficie

nt,

o (10-3

cm

-1/a

tm)

13CH4(4) by N2: freq. shift

R(2) F2

R(2) E

o(T) = o(To) + x(T-To)

o(T) = o(To) + |x(T-To)|

oN

2

: This Worko

air, HITRAN 2008

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.


R(2) Comparison with Other Results


Source Broadener T range (K) Width Width Tdep Shift Shift Tdep13CH4 R2 F2 1 (1313.722 cm−1)HITRAN08 [38] air 210 to 314 0.0620 0.80 −0.00202Smith et al. [43] air 296 0.06325(5) −0.00213(6)Malathy Devi et al. [44] air 296 0.0620(1) −0.0021(2)Present Work N2 80 to 296 0.06191(12) 0.8874(27) −0.00168(13) 0.7(1)E-0512CH4 R2 F2 1 (1322.085 cm−1)HITRAN08 [38] air 296 0.0650 0.84 −0.00160Smith et al. [42] air 210 to 314 0.0650(4) 0.840(4) −0.00160(4) 0.4(1)E-05Smith et al. [45] N2 211 to 298 0.06491(22) 0.842(14) −0.00167(17) 1.0(2)E-05

13CH4 R2 E 1 (1313.788 cm−1)HITRAN08 [38] air 210 to 314 0.0547 0.80 −0.00202Smith et al. [43] air 296 0.05467(6) −0.00226(6)Malathy Devi et al. [44] air 296 0.0547(2) −0.0024(2)Present Work N2 80 to 296 0.05309(13) 0.8603(36) −0.00129(15) 2.2(2)E-0512CH4 R2 E 1 (1322.154 cm−1)HITRAN08 [38] air 296 0.0560 0.80 −0.00160Smith et al. [42] air 210 to 314 0.0560(1) 0.800(4) −0.00160(4) 1.6(1)E-05Smith et al. [45] N2 211 to 298 0.05521(21) 0.855(15) −0.00141(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 manifoldsFitting residuals (upper) and observed spectra (lower) for R(1)▼


Results vs. T for R(0) and R(1)

R(0) and R(1) Comparison with Other Results


Source Broadener T range (K) Width Width Tdep Shift Shift Tdep13CH4 R0 A1 1 (1303.249 cm−1)HITRAN08 [38] air 210 to 314 0.0532 0.63 −0.00201Smith et al. [43] air 296 0.0527(1) −0.00292(6)Malathy Devi et al. [44] air 296 0.0524(1) −0.0032(3)Present Work N2 80 to 296 0.0523(1) 0.679(3) −0.0013(1) 5.2(1)E-0512CH4 R0 A1 1 (1311.432 cm−1)HITRAN08 [38] air 210 to 314 0.0547 0.70 −0.0027Smith et al. [42] air 210 to 314 0.0547(0) 0.70(0) −0.0027(0) 1.6(0)E-05Smith et al. [45] N2 211 to 298 0.05417(11) 0.709(8) −0.00247(11) 2.26(14)E-05Lepere et al. (2002) N2 188 to 297 0.055 0.67/0.71

13CH4 R1 F1 1 (1308.551 cm−1)HITRAN08 [38] air 210 to 314 0.0605 0.80 −0.00201Smith et al. [43] air 296 0.0610(0) −0.00199(4)Malathy Devi et al. [44] air 296 0.0605(1) −0.0017(2)Present Work N2 80 to 296 0.0602(1) 0.869(2) −0.0006(1) 2.3(1)E-0512CH4 R1 F1 1 (1316.827 cm−1)HITRAN08 [38] air 210 to 314 0.0625 0.82 −0.0014Smith et al. [42] air 210 to 314 0.0625(0) 0.82(0) −0.0014(0) 1.2(0)E-05Smith et al. [45] N2 211 to 298 0.06288(10) 0.825(7) −0.00096(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 KPreliminary, work in progress

Transition γ0 n δ0 δ′ No. Spectra

R0 A1 1 (1303.249 cm-1) 0.0523(1) 0.679(3) −0.0013(1) +5.2(1)E-05 9R1 F1 1 (1308.551 cm-1) 0.0602(1) 0.869(2) −0.0006(1) +2.3(1)E-05 9R2 F2 1 (1313.722 cm-1) 0.0619(1) 0.887(3) −0.0017(1) +7(1)E-06 9R2 E 1 (1313.788 cm-1) 0.0531(1) 0.860(4) −0.0013(2) +2.3(2)E-05 9R3 A2 1 (1318.635 cm-1) 0.0555(1) 0.773(4) −0.0011(1) +1.6(1)E-05 9

0.0556(1) 0.787(4) −0.0013(1) +1.0(2)E-05 9*R3 F2 1 (1318.810 cm-1) 0.0651(2) 0.805(6) +0.0025(2) −1(3)E-07 9

0.0644(2) 0.828(5) −0.0044(2) −2.1(3)E-05 9*R3 F1 1 (1318.957 cm-1) 0.0663(2) 0.782(5) −0.0040(2) +7.1(2)E-05 9

0.0657(2) 0.842(2) +0.0017(2) +5.3(2)E-05 9*

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.


Summary and Future Work

Measured and observed• Line widths and pressure-induced shifts for 13CH4/N2 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 13CH4 manifolds• Results to date agree with other measurements of 13CH4 and 12CH4 broadened by N2 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 N2-broadening and shifts.


The Team and Acknowledgements

AcknowledgementsResearch 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 LindaTim

Arlan Mary Ann Chris


Documents

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