1. A. M. Daly, B. J. Drouin, J. C. Pearson, K. Sung, L. R. Brown
Low-temperature high-resolution infrared spectrum of ethane-d1, C2H5D: Rotational analysis of the ν17 band near 805 cm-1 using ERHAM
P. Groner
Department of Chemistry, University of Missouri - Kansas City, Kansas City, MO, USA
A. M. Daly, B. J. Drouin, J. C. Pearson, K. Sung, L. R. Brown
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
A. W. Mantz
Department of Physics, Astronomy and Geophysics, Connecticut College, New London, CT, USA
M. A. H. Smith
Science Directorate, NASA Langley Research Center, Hampton, VA, USA
International Symposium on Molecular Spectroscopy, June 22-26, 2015

2. International Symposium on Molecular Spectroscopy, June 22-26, 2015
IR Spectrum
Spectrum Details Bruker 125HR FT spectrometer at JPL Spectral range cm-1 Temperature K Pressure 5.1 torr Cell path length m Resolution cm-1 (unapodized) Impurities CH3CH3 (≈ 2 %)
International Symposium on Molecular Spectroscopy, June 22-26, 2015

3. International Symposium on Molecular Spectroscopy, June 22-26, 2015
IR Spectrum of C2H5D
Why analysis with ERHAM?
* Analysis with SPFIT is quite successful
(preceding presentation TG01 by Adam Daly)
* Initial purpose: Analysis of 715 cm-1 band (ν11)
However: ν11 level severely disturbed by 3ν18 level
No useful results so far with modified ERHAM (allowing for interactions between different vibrational levels)
* Therefore, try ERHAM with less perturbed ν17 at 805 cm-1
International Symposium on Molecular Spectroscopy, June 22-26, 2015

4. Origin of perturbations: Excited states of ν18
Torsional potential function
Daly et al., J. Mol. Spectrosc. (2015) 307, 27-32
Torsional energy levels (J = 0)
A state +
E state +
ν11, ν17
K ≠ 0 states limited by red line and A state
ΔE a
νobs
Uncertainty
νobs - νcalc
Weighted residual
2A - 0A
515.1 b
1.0
2.129
2E - 0E
0.047
3E - 1E
440.1 b
-2.918
3A - 1A
463.1 b
0.199
4A - 2A
336.5 b
2.192
4E - 2E
390.0 b
1.022
0E - 0A
74.167
0.018
0.000
-0.008
1E - 1A
0.342
0.006
Coefficient
This work
V3 / cm-1
(44)
V6 / cm-1
7.09(12)
F / cm-1 (constant)
International Symposium on Molecular Spectroscopy, June 22-26, 2015

5. International Symposium on Molecular Spectroscopy, June 22-26, 2015
Analysis
Ground state spectroscopic constants (including ρ and β) fixed to results of rotational analysis of GS and first torsional excited state ν18
[Daly et al., J. Mol. Spectrosc. (2015) 307, 27-32]
ERHAM analysis based on SPFIT assignments more difficult than expected
A-E splittings GS: up to ± cm-1 ≈ unapodized resolution
A-E splittings ν18 state: up to ± cm-1
Problems
* Labeling and tracking K-assignments of E levels
* Inconsistencies within combination differences / upper state energies
International Symposium on Molecular Spectroscopy, June 22-26, 2015

6. Upper state energies* / Combinations differences
* Eu = El,calc + νobs Standard deviations s of Eu for a given level are typically < cm-1 Cases with “outliers” (example for 0/A state below) Cases with 4 to 8 results spread ~ regularly over cm-1 Cases were 6 to 10 results split into 2 groups, each group with s < cm-1, group separation > cm-1 (example for 1/E state below) σ J’ n’ J” n”
ν obs Eu
obs-calc
average
std. dev 9 5 6 8 7
0.0002 10
0.0012 1 3 2
0.0009
0.0004
0.0003
International Symposium on Molecular Spectroscopy, June 22-26, 2015

7. International Symposium on Molecular Spectroscopy, June 22-26, 2015
Results
Weighted least squares fit
Weight = inverse square of experimental uncertainty
5041 transitions assigned
2158 A-state transitions (non-zero weight)
2834 E-state transitions (non-zero weight)
No frequencies assigned to more than one transition
ρ ,β, & GS parameters fixed to values from rotational spectroscopy (MW to THz) [a]
1.161 weighted standard deviation ( cm-1 for most transitions)
24 variable spectroscopic constants
8 rotational & quartic centrifugal distortion constants
1 vibrational energy ( (23) cm-1)
3 tunneling energy parameters
6 Coriolis-type and Dab tunneling parameters
6 tunneling contribution to rotational & quartic distortion constants
[a] [Daly et al., J. Mol. Spectrosc. (2015) 307, 27-32]
[a] Daly et al., J. Mol. Spectrosc. (2015) 307, 27-32
International Symposium on Molecular Spectroscopy, June 22-26, 2015

8. International Symposium on Molecular Spectroscopy, June 22-26, 2015
Results
Parameter
Ground state
ν17 State ρ
(69)
β (deg)
0.905(63)
A (MHz)
(24)
(18)
[ga]1 (MHz)
-2.842(84)
B (MHz)
(89)
(72)
[gaK]1 (MHz)
(52)
C (MHz)
(89)
(75)
[gaJ]1 (MHz)
(11)
-DJ (kHz)
(18)
(18)
[gb]1 (MHz)
-21.5(22)
-DJK (kHz)
(65)
60.178(20)
[gbJ]1 (MHz)
(19)
-DK (kHz)
(41)
(79)
[Dab]1 (MHz)
5.73(26)
-d1 (kHz)
(29)
0.9094(29)
[A-(B+C)/2]1 /kHz
9.11(24)
-44(12)
d2 (kHz)
(19)
0.0656(13)
[(B+C)/2]1 /kHz
-1.07(16)
-2.30(62)
HJ (Hz)
0.0027(11)
[B-C)/4]1 /kHz
0.749(91)
-25.3(22)
HJK (Hz)
0.2022(48)
[DK]1 /kHz
-0.118(60)
HKJ (Hz)
-0.021(31)
[d1]1 /kHz
0.0266(18)
HK (Hz)
4.69(18)
[d2]1 /kHz
(79)
ε0 (cm-1)
(23) s
1.1612
ε1 (MHz)
-24.74(69)
80.13(44)
ε2 (MHz)
0.0153(43)
21.62(29)
ε3 (MHz)
2.26(24)
International Symposium on Molecular Spectroscopy, June 22-26, 2015

9. International Symposium on Molecular Spectroscopy, June 22-26, 2015

10. International Symposium on Molecular Spectroscopy, June 22-26, 2015

11. International Symposium on Molecular Spectroscopy, June 22-26, 2015
Discussion
Satisfactory analysis of 805 cm-1 band with ERHAM Remaining problems Discrepancies of Eu, K-labeling of energy levels: need diligence ρ-vector parameters (ρ, β): fixed at GS/ν18, but could be different in ν11. LS fit with variable ρ, β: perfect correlation between ρ and ε0. Transition frequency accuracy below cm-1 seems possible = prerequisite to identify source of minor intensity perturbations observed in high-K R-branch transitions
International Symposium on Molecular Spectroscopy, June 22-26, 2015

12. International Symposium on Molecular Spectroscopy, June 22-26, 2015
Thank you
International Symposium on Molecular Spectroscopy, June 22-26, 2015