Transcript Col_05_OCS.ppt

Measurements of N2- and O2-pressure
broadening and pressure-induced shifts
for 16O12C32S transitions in the 3 band
M.A. Koshelev and M.Yu. Tretyakov
Institute of Applied Physics, Russian Academy of Sciences,
Nizhnii Novgorod, Russia
R.M. Lees and Li-Hong Xu
CLAMS, CIPI and Department of Physical Sciences,
University of New Brunswick, Saint John, NB, Canada
Motivations

OCS is the major reservoir of atmospheric sulphur, so is a
species of considerable environmental importance.

OCS is a significant astronomical molecule, observed in
interstellar clouds, comets and planetary atmospheres.

Retrieval of reliable column densities from remote sensing in
the atmosphere and astronomical sources requires accurate
line profiles, pressure shift coefficients and intensities.

OCS has the strong 3 absorption band in the 5 mm operating
region of our lead salt diode laser, and has a rich spectrum of
isotopic and combination band lines to give good calibration.
TDL IR Spectrometer for Line Broadening
Lead-salt
5 mm TDL
Lead-salt diode laser source - dual-cell frequency
calibration scheme - multiplexed data acquisition.
Sample and multiplexed calibration signals
OCS + O2
O2-broadened OCS R(40) line at 2073.7287 cm-1
Frequency Calibration for the R(40) OCS Line
Map of point index
of reference peaks
against absolute
frequencies.
Fourth-order
polynomial fit to the
reference points
Fit residuals x 1000
Pressure Dependence of O2-Broadening
for the R(40) Line of OCS
Fitting to N2-broadened R(40) line of OCS
Fit to Voigt profile
+ background
Fitted HWHM
0.00772(1) cm-1
Pressure Dependence of OCS Line Widths
0.0953(10) cm-1/atm
0.0745(10) cm-1/atm
1-s
Error
bars
J-Dependence of the Broadening Coefficients
OCS-N2
OCS-O2
Comparison with Previous Results
v1 Data:
A. Mouchet et al.,
Can. J. Phys. 63, 527 (1985)
J.-P. Bouanich et al.,
J. Mol. Spec. 123, 37 (1987)
2v3 Data:
J.L. Domenech et al.,
J. Mol. Spec. 200, 266 (2000)
Grey zones
represent
3-s limits
Pressure-Induced Frequency Shift
Std Ref
Frequency
Slope = – 0.0019(2) cm-1/atm
[Error bars are 1-s uncertainties]
Conclusions

Pressure-broadening parameters measured for OCS in the 3
band to better than 1.5% for mixtures with N2 and O2.
Measured parameters agree well with previous values for the
v1 and 2v3 bands.

Pressure-broadening parameters decrease by over 20% from
low J up to J of ~50.

OCS-N2 broadening parameters are larger than OCS-O2 by
about 13% at low J – difference is ~ independent of J.

Small negative pressure-induced line shifts are observed for
OCS broadened by N2 and O2.