CARS spectroscopy of molecules in supersonic free jets

Abstract

CARS spectra are reported for N2, O2, H2, D2, C2H4, and various mixtures cooled by supersonic jet expansion. Analysis of the Q branch structure of the diatomic molecules permits direct measurement of rotational populations, temperatures, and densities as a function of position in the free jet zone. Good agreement is obtained with temperature results for N2 from electron beam fluorescence studies and with densities calculated from the customary isentropic expansion equations. The detection sensitivity was sufficient that, for the first time, broadband CARS spectra were obtained for a molecular beam (D2). A simple relaxation model of the expansion process yields rotational collision numbers of 10±4 And 14±4 for N2 and O2 but these values may be high because of condensation heating. The model was not successful in treating the rotational relaxation of D2 and H2 but temperature measurements show qualitatively that D2 ⋅⋅⋅ X transfer efficiency increases in the order X = D2<He<Ar<CH4.

Formation of Large Ag Clusters with Shells of Methane, Ethylene, and Acetylene in He Droplets

“… a All values are in inverse centimeters. IR designates infrared active modes; R indicates Raman active modes. b Reference . c Reference . d References and . e Reference for solid in phase I; see also reference . f Reference in solid II ethane and ethane- d 6 the band ν 10 is split due to crystalline force field, see reference . g Reference . h Band is split in orthorhombic phase by crystalline field, reference . i Deperturbed values from reference . j Reference for 83 K and 63 K ν 3 = 3226.3; reference . k Reference . l Reference at 63 K. m Reference . n The band is split due to crystalline force field; reference . o Reference . p Reference . q References and . r Reference . …”

Low-Temperature Rotational Relaxation of N2 Studied with Resonance-Enhanced Multiphoton Ionization

“…Further measurements of the rotational temperature in free jets of nitrogen from room temperature sources from various Raman techniques − are also available in the literature (not shown in Figure ). All these data are in good agreement with the temperatures predicted from the σ r ( T t ) of this work.…”

Molecular Relaxation in Supersonic Free Jets of N2 and CH4 from Stimulated Raman Spectroscopy and Time-of-Flight Measurements

“…A wide variety of experimental techniques have been applied for the determination of rotational temperatures in free jets of N 2 ; these techniques include energy balance in conjunction with time-of-flight measurements, ,, spontaneous Raman scattering, coherent anti-Stokes Raman spectroscopy (CARS), , electron beam induced fluorescence, ,− and resonance-enhanced multiphoton spectroscopy (REMPI) CARS, stimulated Raman spectroscopy (SRS), and Fourier transform infrared (FTIR) spectroscopy …”