1. Measurements of N 2 - and O 2 -pressure broadening and pressure-induced shifts for 16 O 12 C 32 S 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

2. 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  m operating region of our lead salt diode laser, and has a rich spectrum of isotopic and combination band lines to give good calibration.

3. TDL IR Spectrometer for Line Broadening Lead-salt diode laser source - dual-cell frequency calibration scheme - multiplexed data acquisition. Lead-salt 5  m TDL

4. Sample and multiplexed calibration signals OCS + O 2 O 2 -broadened OCS R(40) line at 2073.7287 cm ‑ 1

5. Frequency Calibration for the R(40) OCS Line Map of point index of reference peaks against absolute frequencies. Fit residuals x 1000 Fourth-order polynomial fit to the reference points

6. Pressure Dependence of O 2 -Broadening for the R(40) Line of OCS

7. Fitting to N 2 -broadened R(40) line of OCS Fitted HWHM 0.00772(1) cm -1 Fit to Voigt profile + background

8. Pressure Dependence of OCS Line Widths 0.0953(10) cm -1 / atm 0.0745(10) cm -1 / atm 1-  Error bars

9. J-Dependence of the Broadening Coefficients OCS-N 2 OCS-O 2

10. Comparison with Previous Results Grey zones represent 3-  limits v 1 Data: A. Mouchet et al., Can. J. Phys. 63, 527 (1985) J.-P. Bouanich et al., J. Mol. Spec. 123, 37 (1987) 2v 3 Data: J.L. Domenech et al., J. Mol. Spec. 200, 266 (2000)

11. Pressure-Induced Frequency Shift Slope = – 0.0019(2) cm -1 / atm [Error bars are 1-  uncertainties] Std Ref Frequency

12. Conclusions  Pressure-broadening parameters measured for OCS in the 3 band to better than 1.5% for mixtures with N 2 and O 2. Measured parameters agree well with previous values for the v 1 and 2v 3 bands.  Pressure-broadening parameters decrease by over 20% from low J up to J of ~50.  OCS-N 2 broadening parameters are larger than OCS-O 2 by about 13% at low J – difference is ~ independent of J.  Small negative pressure-induced line shifts are observed for OCS broadened by N 2 and O 2.