The molecular beam opto-thermal infrared spectroscopy [l] has been recently applied for studying the infrared multiple-photon absorption (M.P.A.) of polyatomic molecules [2J. The main advantage of this method, compared with conventional cell experiments, is the complete removal of collisional effects. The low density molecular beam virtually eliminates other sources of systematic error like, for example, the self-focusing and de-focusing of the laser beam which is sometimes observed in cell experiments [3]. Moreover the molecular beam technique has the following unique feature: it is possible to prepare molecules with different distributions of rovibronic states. We shall show later how this last property may be used for studying the effect of the initial distribution of internal energy on the M.P.A. process. The experimental apparatus and the detection system are described elsewhere [2,4]. In the present configuration, the molecular beam is produced by expanding pure SF` or CF^Br seeded in He through a variable-temperature supersonic nozzle (diameter 75 ±_ 5μm). The temperature may be set from about 100 K to 500 K and is stabilized within 0.1 K. The IR pulsed source is a Lumonics TEA 820 line-tunable CO2 laser. The laser fluence may be varied by means of a suitable optical system and is measured by a Scientech powermeter. The molecular beam energy distribution may be varied by changing both the pressure and the temperature of the source. The translational energy distribution has been determined by time-of—flight measurements [4].

Infrared multiple-photon absorption of SF6 and CF3Br in a variable temperature molecular beam

Zen, Mario;Boschetti, Andrea;
1993

Abstract

The molecular beam opto-thermal infrared spectroscopy [l] has been recently applied for studying the infrared multiple-photon absorption (M.P.A.) of polyatomic molecules [2J. The main advantage of this method, compared with conventional cell experiments, is the complete removal of collisional effects. The low density molecular beam virtually eliminates other sources of systematic error like, for example, the self-focusing and de-focusing of the laser beam which is sometimes observed in cell experiments [3]. Moreover the molecular beam technique has the following unique feature: it is possible to prepare molecules with different distributions of rovibronic states. We shall show later how this last property may be used for studying the effect of the initial distribution of internal energy on the M.P.A. process. The experimental apparatus and the detection system are described elsewhere [2,4]. In the present configuration, the molecular beam is produced by expanding pure SF` or CF^Br seeded in He through a variable-temperature supersonic nozzle (diameter 75 ±_ 5μm). The temperature may be set from about 100 K to 500 K and is stabilized within 0.1 K. The IR pulsed source is a Lumonics TEA 820 line-tunable CO2 laser. The laser fluence may be varied by means of a suitable optical system and is measured by a Scientech powermeter. The molecular beam energy distribution may be varied by changing both the pressure and the temperature of the source. The translational energy distribution has been determined by time-of—flight measurements [4].
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11582/2919
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