Intrapulse quantum cascade laser spectrometers are able to produce both saturation and molecular alignment of the gas sample. This is due to the rapid sweep of the radiation through the absorption features. The intrapulse time domain spectra closely resemble those recorded in coherent optical nutation experiments. In the present paper, the frequency down-chirped technique is employed to investigate the nitrous oxide–foreign gas collisions. We have demonstrated that the measurements may be characterized by the induced polarization dominated and collision dominated measurement limits. The first of these is directly related to the time dependence of the long range collision cross sections. Among the collisional partners considered, carbon dioxide shows a very unusual behavior of rapid polarization damping, resulting in the production of symmetrical line shapes at very low gas buffer pressures. In the collision dominated regime, the pressure broadening parameters, which we have derived, are comparable at slow chirp rates, with those derived from other experimental methods. By comparing the pressure broadening coefficients of Ar, , and with those of He, making use of the chirp rate independence of the pressure broadening by helium, we have shown that at higher chirp rates there is clear evidence of the chirp-rate dependence of the pressure broadening parameters of and .
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28 April 2010
Research Article|
April 22 2010
Time dependent measurements of nitrous oxide and carbon dioxide collisional relaxation processes by a frequency down-chirped quantum cascade laser: Rapid passage signals and the time dependence of collisional processes
Nicola Tasinato;
Nicola Tasinato
1Dipartimento di Chimica Fisica,
Università Ca' Foscari di Venezia
, Calle Larga Santa Marta 2137, I-30123 Venezia, Italy
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Kenneth G. Hay;
Kenneth G. Hay
2Department of Physics, SUPA,
University of Strathclyde
, John Anderson Building, 107 Rottenrow, Glasgow G4 0NG, United Kingdom
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Nigel Langford;
Nigel Langford
2Department of Physics, SUPA,
University of Strathclyde
, John Anderson Building, 107 Rottenrow, Glasgow G4 0NG, United Kingdom
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Geoffrey Duxbury;
Geoffrey Duxbury
a)
2Department of Physics, SUPA,
University of Strathclyde
, John Anderson Building, 107 Rottenrow, Glasgow G4 0NG, United Kingdom
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David Wilson
David Wilson
2Department of Physics, SUPA,
University of Strathclyde
, John Anderson Building, 107 Rottenrow, Glasgow G4 0NG, United Kingdom
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a)
Electronic mail: g.duxbury@strath.ac.uk.
J. Chem. Phys. 132, 164301 (2010)
Article history
Received:
September 19 2009
Accepted:
March 19 2010
Citation
Nicola Tasinato, Kenneth G. Hay, Nigel Langford, Geoffrey Duxbury, David Wilson; Time dependent measurements of nitrous oxide and carbon dioxide collisional relaxation processes by a frequency down-chirped quantum cascade laser: Rapid passage signals and the time dependence of collisional processes. J. Chem. Phys. 28 April 2010; 132 (16): 164301. https://doi.org/10.1063/1.3386385
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