Transcript (1,1) band of O2.pptx

Improved Experimental Line
Positions for the (1,1) Band of the
b 1Σ+g - X 3Σ-g Transition of O2 by
Intracavity Laser Absorption
Spectroscopy
Leah C. O'Brien, Southern Illinois University,
Edwardsville, IL 62026-1652;
Emily C. O'Brien and James J. O'Brien, University of
Missouri, St. Louis, MO 63121
The Atmospheric A Band of O2
 The weak b 1Σ+g - X 3Σ–g transition in the far red is designated as the
atmospheric A band in the solar spectrum
 This transition is spin forbidden and electric-dipole forbidden.
 As early as 1927 this transition was described as atmospheric
absorption in the solar emission spectrum, where the long
atmospheric path length enabled the detection of these weak spectral
features (Dieke and Babcock; Babcock).
 The most comprehensive spectroscopic study to date on the
atmospheric A bands is still that by Babcock and L. Herzberg (1948):
this work presents the line positions, assignments and molecular
constants observed from the analysis of the (0,0), (1,0), (2,0), (3,0),
(1,1), (2,1), and (3,1) bands of 16O2, and the (0,0) and (1,0) bands of
16O18O and 16O17O.
Recent work on the (0,0), (1,0)
and/or (2,0) bands
 A.J. Phillps, F. Peters, and P.A. Hamilton, J. Mol. Spectrosc. 14 (1997) 162-166.
 S.-L. Cheah, Y.-P. Lee, and J.F. Ogilvie, JQSRT 64 (2000) 467-482.
 L.R. Brown, C. Plymate, J. Mol. Spectrosc. 199 (2000) 116-179.
 S.F. Yang, M.R. Canagaratna, S.K. Witonsky, S.L. Coy, J.I. Steinfeld, R.W. Field
and A.A. Kachanov, J. Mol. Spectrosc. 201 (2000) 188-197.
 L.C. O’Brien, H. Cao and J.J. O’Brien, J. Mol. Spectrosc. 207 (2001) 99-103.
 D.J. Robichaud, J.T. Hodges, P. Maslowski, L.Y. Yeung, M. Okamura, C.E. Miller,
and L.R. Brown, J. Mol. Spectrosc. 251 (2008) 27-37.
 D. Lisak, P. Maslowski, A. Cygan, K. Bielska, S. Wojtewica, M. Piwinski, J.T.
Hodges, R.W. Trawinsky and R. Ciurylo, Phys. Rev. 81 (2010) 042504:1-10.
 D. A. Long, D. K. Havey, M. Okumura, C. E. Miller3 and J. T. Hodges, Phys. Rev.
A 81, 064502 (2010).
 I.E. Gordon, L.S. Rothman, G.C. Toon, JQSRT 112 (2011) 2310-2322.
Previous experimental work on
the (1,1) band
 In 1927 Babcock estimated the intensity of the (1,1) band of the
b 1Σ+ - X 3Σ– transition was 1/2500 the intensity of the (0,0)
band of this transition.
 H.D. Babcock, Phys. Rev. 35 (1930) 125.
 R. Mecke and W. Baumann, Zs. f. Phys. 73 (1932) 139-146.
 H.D. Babcock and L. Herzberg, Ap. J. 108 (1948) 167-190.
 N. J. van Leeuwen, H.G. Kjaergaard, D.L. Howard and A.C.
Wilson, J. Mol. Spectrosc. 228 (2004) 83-91.
 Prediction of (1,1) line positions by I.E. Gordon, L.S.
Rothman, G.C. Toon, JQSRT 112 (2011) 2310-2322
Based on (1,0) band measurements and IR/microwave work of Rouillé et
al.
Intracavity Laser Absorption Spectroscopy
 Absorption spectra recorded using intracavity laser spectrometer at the
University of Missouri – St. Louis
 Configured with a hollow cathode plasma discharge, 3 A from RPG power
supply
 Plasma discharge was used to enhance absorption from v=1 in the ground state of oxygen
to record the (1,1) band the b 1Σ+ - X 3Σ–transition of oxygen: absorption for the (0,0)
band features also were enhanced
 Pressures of 4-8 Torr of oxygen were employed, so that the plasma
discharge formed primarily outside of the hollow cathode
 Generation times (tg) up to 200 µs were used, the copper hollow cathode
was 50 mm long, the overall laser cavity length was 2.30 m and the section
of the cavity containing oxygen was 1.81 m
 Spectra are recorded as a series of overlapping spectral segments, each
segment being ̴ 6 cm−1 wide
Calibration
 Calibration is accomplished by alternatively measuring the spectrum of the intracavity O2
species and an I2 absorption spectrum recorded from an extra-cavity iodine cell heated to
approximately 590 C
 Part 1 (11400 – 13010 cm-1) of the widely used Iodine Atlas served as reference
 Used relationship between the dispersion determined for the diode array detector at the
central channel and the central channel position in wavenumbers for a given grating order:
for the specific iodine spectra used to calibrate the oxygen lines reported herein, iodine
reference lines were selected such that the dispersion determined for the diode array detector
was consistent with the established linear relationship for this region
 In total, spectra were collected at 33 separate spectrometer grating positions, and the
dispersion ranged from 0.00602 cm-1/channel at 12838 cm-1 to 0.00646 cm-1/channel at
13015 cm-1: this method provided a self-consistent check that the most appropriate Iodine
reference lines were selected from the Iodine Atlas
 Peak positions are determined from the zero crossing-points of the first derivative spectra
using Savitzky–Golay polynomial smoothing: the procedure enables the positions for
isolated, unblended lines to be determined to an accuracy of better than ±0.005 cm−1
 Spectra of the (1,1) band of the b 1Σ+ - X 3Σ– transition were collected on 3 separate days,
and the peak positions used in the fit were the average of the measured line positions
Dispersion vs. Wavenumber at Channel 512
Plasma-enhanced absorption from v″=1
4 spectra are collected at every monochromator
position
Background: no oxygen, no plasma
Iodine: no oxygen, no plasma
Oxygen-no-plasma: ~4 torr oxygen
Oxygen-with-plasma: ~4 torr oxygen
Oxygen-with-plasma showed increased absorption for
oxygen for v″=0,1
New!
Analysis of the (1,1) band
 Assignments were
straightforward based on the
work of van Leeuwen et al.
 A nonlinear least-squares
program was used to fit the
line positions to standard
energy level expressions. For
the b 1Σ+g state, the energy
levels are given by E(J) = Tv +
BvJ(J + 1) – DvJ2(J + 1)2 +
HvJ3(J + 1)3.
 For the v″=1 in the X 3Σ–g
ground state, the energy level
expressions given in Rouillé et
al. were employed.
5. H.D. Babcock and L. Herzberg, Ap.
J. 108 (1948) 167-190.
Line list for (1,1) band
J"
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
PP(J")
12966.4177
*12960.4200
12954.0672
12947.3018
12940.1638
12932.6265
12924.7019
12916.3817
12907.6731
12898.5807
12889.0895
12879.2019
12868.9291
12858.2511
12847.1862
obs-calc
-0.0031
0.0205
-0.0031
-0.0088
0.0019
0.0022
0.0043
0.0003
-0.0022
0.0023
-0.0002
-0.0061
-0.0027
-0.0082
-0.0026
*blended line, deweighted in fit
RR(J")
12974.6677
12979.6544
12984.2698
12988.4879
12992.2965
12995.7163
12998.7326
13001.3430
*13003.5394
13005.3433
13006.7368
13007.7077
13008.2562
13008.3855
13008.0885
13007.3600
13006.1917
13004.5880
obs-calc
0.0092
-0.0058
0.0015
0.0066
-0.0010
0.0014
0.0014
-0.0010
-0.0114
-0.0052
0.0026
0.0031
0.0003
0.0009
0.0020
0.0025
-0.0013
-0.0004
Linelist for (1,1) band
J"
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
PQ(J")
*12962.5157
12956.0858
12949.2796
12942.1129
12934.5546
12926.6031
12918.2635
12909.5382
12900.4253
12890.9159
12881.0179
12870.7193
*12860.0100
12848.9423
obs-calc
-0.0104
0.0011
-0.0079
0.0018
0.0048
0.0014
-0.0019
-0.0019
0.0009
-0.0015
0.0003
-0.0043
-0.0235
-0.0031
*blended line, deweighted in fit
RQ(J")
12976.5334
12981.6168
12986.2678
*12990.4714
12994.3512
12997.7830
13000.8156
13003.4502
13005.6752
13007.4972
13008.8970
13009.8900
13010.4589
13010.6024
13010.3219
13009.6108
*13008.4487
13006.8772
obs-calc
-0.0102
0.0002
0.0055
-0.0318
0.0080
0.0009
-0.0031
-0.0009
-0.0017
0.0039
-0.0004
0.0040
0.0035
0.0004
0.0001
0.0002
-0.0152
0.0021
Summary
 The (1,1) band of the b 1Σ+ - X 3Σ– transition of O2 was
recorded by ILS
 The rms residual for the strong, unblended lines obtained in
the fit is 0.0025 cm-1
 The accuracy of the previous experimental data set by van Leeuwen et
al. was estimated at 0.02 cm-1, and thus our work represents a
significant improvement in the accuracy and precision of experimental
line positions.
 Comparison to the (1,1) band line list that was calculated by
Gordon et al. shows:
 Average discrepancy in line position was found to be 0.0004 cm-1
 RMS deviation in line position was found to be 0.0048 cm-1
 A new method of producing vibrational hot molecules for
absorption spectroscopy is described
Acknowledgements
National Science Foundation
Emily O’Brien, summer
undergraduate researcher
(from University of Missouri
– Columbia)
Thank you for your
attention!