LOW-TEMPERATURE SPECTROSCOPY OF THE {sup 12}C{sub 2}H{sub 2} (υ{sub 1} + υ{sub 3}) BAND IN A HELIUM BUFFER GAS
- 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)
- INFN, Istituto Nazionale di Fisica Nucleare, Sez. di Firenze, Via G. Sansone 1, I-50019 Sesto Fiorentino (Italy)
Buffer gas cooling with a {sup 4}He gas is used to perform laser-absorption spectroscopy of the {sup 12}C{sub 2}H{sub 2} (υ{sub 1} + υ{sub 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 {sup 12}C{sub 2}H{sub 2} in the buffer cell is measured against the {sup 4}He 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: σ{sub el}(100 K) = (4 ± 1) × 10{sup –20} m{sup 2} and σ{sub el}(25 K) = (7 ± 2) × 10{sup –20} m{sup 2}.
- OSTI ID:
- 22521387
- Journal Information:
- Astrophysical Journal, Vol. 801, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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