Low-temperature spectroscopy of the (C2H2)-C-12 (upsilon(1) + upsilon(3)) band in a helium buffer gas

Year: 2015

Authors: Santamaria L., Di Sarno V., Ricciardi I., De Rosa M., Mosca S., Santambrogio G., Maddaloni P., De Natale P.

Autors Affiliation: CNR-INO, Istituto Nazionale di Ottica, Via Campi Flegrei 34, I-80078 Pozzuoli, Italy
CNR-INO, Istituto Nazionale di Ottica, Via N. Carrara 1, I-50019 Sesto Fiorentino, Italy
Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany
INFN, Istituto Nazionale di Fisica Nucleare, Sez. di Firenze, Via G. Sansone 1, I-50019 Sesto Fiorentino, Italy
CNR-INO, Istituto Nazionale di Ottica, Largo E. Fermi 6, I-50125 Firenze, Italy

Abstract: Buffer gas cooling with a He-4 gas is used to perform laser-absorption spectroscopy of the (C2H2)-C-12 (upsilon(1) + upsilon(3)) band at cryogenic temperatures. Doppler thermometry is first carried out to extract translational temperatures from the recorded spectra. Then, rotational temperatures down to 20 K are retrieved by fitting the Boltzmann distribution to the relative intensities of several ro-vibrational lines. The potential of our setup to tune the thermal equilibrium between translational and rotational degrees of freedom is also demonstrated. This can be used to reproduce in a controlled way the regime of non-local thermal equilibrium typically encountered in the interstellar medium. The underlying helium-acetylene collisional physics, relevant for modeling planetary atmospheres, is also addressed. In particular, the diffusion time of (C2H2)-C-12 in the buffer cell is measured against the He-4 flux at two separate translational temperatures; the observed behavior is then compared with that predicted by a Monte Carlo simulation, thus providing an estimate for the respective total elastic cross sections: sigma(el)(100 K) = (4 +/- 1) x 10(-20) m(2) and sigma(el)(25 K) = (7 +/- 2) x 10(-20) m(2).


Volume: 801 (1)      Pages from: 50-1  to: 50-6

More Information: The authors acknowledge technical support by G. Notariale. This work was funded by MIUR-FIRB project RBFR1006TZ and by INFN project SUPREMO.
KeyWords: Instrumentation: miscellaneous; ISM: molecules; methods: laboratory: molecular; Planets and satellites: atmospheres; Techniques: miscellaneous
DOI: 10.1088/0004-637X/801/1/50

Citations: 12
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