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
1
IR Spectrum
Spectrum Details
Bruker 125HR FT spectrometer at JPL
Spectral range 650 - 1530 cm-1
Temperature
130.52 K
Pressure
5.1 torr
Cell path length 0.2038 m
Resolution
0.0028 cm-1 (unapodized)
Impurities
CH3CH3 (≈ 2 %)
International Symposium on Molecular Spectroscopy, June 22-26, 2015
2
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
3
Origin of perturbations: Excited states of ν18
Torsional potential function
Daly et al., J. Mol. Spectrosc. (2015) 307, 27-32
ΔE a
νobs
2A - 0A
515.1 b
2E - 0E
515.1 b
3E - 1E
440.1 b
3A - 1A
463.1 b
4A - 2A
336.5 b
4E - 2E
390.0 b
0E - 0A
74.167
1E - 1A
-3382.229
Coefficient
V3 / cm-1
V6 / cm-1
F / cm-1 (constant)
Uncertainty νobs - νcalc
1.0
2.129
1.0
0.047
1.0
-2.918
1.0
0.199
1.0
2.192
1.0
1.022
0.018
0.000
0.342
0.006
This work
1004.561(44)
7.09(12)
9.43489
Weighted residual
2.129
0.047
-2.918
0.199
2.192
1.022
-0.008
0.018
800
300
Torsional energy levels (J = 0)
A state
+
E state
+
ν11, ν17
K ≠ 0 states limited by red line
-60
and A state
-40
-20
0
20
40
60
-200
International Symposium on Molecular Spectroscopy, June 22-26, 2015
4
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:
A-E splittings ν18 state:
up to ±0.0025 cm-1 ≈ unapodized resolution
up to ± 0.011 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
5
Upper state energies* / Combinations differences
* Eu = El,calc + νobs
Standard deviations s of Eu for a given level are typically < 0.001 cm-1
Cases with “outliers” (example for 0/A state below)
Cases with 4 to 8 results spread ~ regularly over 0.002 cm-1
Cases were 6 to 10 results split into 2 groups, each group with s < 0.0004
cm-1, group separation > 0.0010 cm-1 (example for 1/E state below)
σ
J’
n’
J”
n”
0
0
0
1
1
1
1
1
1
1
1
9
9
9
9
9
9
9
9
9
9
9
5
5
5
5
5
5
5
5
5
5
5
9
8
10
10
9
8
10
8
9
10
8
6
7
7
3
2
3
6
6
6
7
7
ν obs
796.8128
807.9441
784.4464
797.5362
810.9642
821.2154
784.4529
807.9505
796.8208
784.4521
807.9499
Eu
867.8080
867.8100
867.8100
867.8117
867.8118
867.8119
867.8121
867.8132
867.8134
867.8136
867.8138
International Symposium on Molecular Spectroscopy, June 22-26, 2015
obs-calc
-0.0018
0.0002
0.0002
-0.0017
-0.0016
-0.0016
-0.0014
-0.0002
0
0.0002
0.0004
average
std. dev
867.8093
0.0012
867.8119
0.0002
0.0009
867.8135
0.0003
6
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 (0.0006 cm-1 for most transitions)
24 variable spectroscopic constants
8 rotational & quartic centrifugal distortion constants
1 vibrational energy (805.341939(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]
International Symposium on Molecular Spectroscopy, June 22-26, 2015
7
Results
Parameter
ρ
β (deg)
A (MHz)
B (MHz)
C (MHz)
-DJ (kHz)
-DJK (kHz)
-DK (kHz)
-d1 (kHz)
d2 (kHz)
HJ (Hz)
HJK (Hz)
HKJ (Hz)
HK (Hz)
ε0 (cm-1)
ε1 (MHz)
ε2 (MHz)
ε3 (MHz)
Ground state
0.4344027(69)
0.905(63)
69653.3910(24)
18859.08109(89)
18214.159883(89)
26.8802(18)
66.3856(65)
245.155(41)
1.01116(29)
0.08252(19)
0.0027(11)
0.2022(48)
-0.021(31)
4.69(18)
-24.74(69)
0.0153(43)
ν17 State
Parameter
70183.543(18)
18803.0694(72)
18191.8103(75)
26.6163(18)
60.178(20)
311.659(79)
0.9094(29)
0.0656(13)
[ga]1 (MHz)
[gaK]1 (MHz)
[gaJ]1 (MHz)
[gb]1 (MHz)
[gbJ]1 (MHz)
[Dab]1 (MHz)
[A-(B+C)/2]1 /kHz
[(B+C)/2]1 /kHz
[B-C)/4]1 /kHz
[DK]1 /kHz
[d1]1 /kHz
[d2]1 /kHz
s
805.341939(23)
80.13(44)
21.62(29)
2.26(24)
Ground state
9.11(24)
-1.07(16)
0.749(91)
International Symposium on Molecular Spectroscopy, June 22-26, 2015
ν17 State
-2.842(84)
0.00320(52)
0.00150(11)
-21.5(22)
-0.0192(19)
5.73(26)
-44(12)
-2.30(62)
-25.3(22)
-0.118(60)
0.0266(18)
0.01006(79)
1.1612
8
International Symposium on Molecular Spectroscopy, June 22-26, 2015
9
International Symposium on Molecular Spectroscopy, June 22-26, 2015
10
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 0.0005 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
11
Thank you
International Symposium on Molecular Spectroscopy, June 22-26, 2015
12