Fourier transform infrared jet spectroscopy using a heated slit source

High-temperature hypersonic Laval nozzle for non-LTE cavity ringdown spectroscopy

A small dimension Laval nozzle connected to a compact high enthalpy source equipped with cavity ringdown spectroscopy (CRDS) is used to produce vibrationally hot and rotationally cold high-resolution infrared spectra of polyatomic molecules in the 1.67 µm region. The Laval nozzle was machined in isostatic graphite, which is capable of withstanding high stagnation temperatures. It is characterized by a throat diameter of 2 mm and an exit diameter of 24 mm. It was designed to operate with argon heated up to 2000 K and to produce a quasi-unidirectional flow to reduce the Doppler effect responsible for line broadening. The hypersonic flow was characterized using computational fluid dynamics simulations, Pitot measurements, and CRDS. A Mach number evolving from 10 at the nozzle exit up to 18.3 before the occurrence of a first oblique shock wave was measured. Two different gases, carbon monoxide (CO) and methane (CH₄), were used as test molecules. Vibrational (T_vib) and rotational (T_rot) temperatures were extracted from the recorded infrared spectrum, leading to T_vib = 1346 ± 52 K and T_rot = 12 ± 1 K for CO. A rotational temperature of 30 ± 3 K was measured for CH₄, while two vibrational temperatures were necessary to reproduce the observed intensities. The population distribution between vibrational polyads was correctly described with T_vib ^I=894±47 K, while the population distribution within a given polyad (namely, the dyad or the pentad) was modeled correctly by T_vib ^II=54±4 K, testifying to a more rapid vibrational relaxation between the vibrational energy levels constituting a polyad.

The reduced cohesion of homoconfigurational 1,2-diols

Homochiral encounters of vicinal diols are blocked from relaxing to the heterochiral global minimum dimer structure in supersonic jet expansions.

Uniform Supersonic Expansion for FTIR Absorption Spectroscopy: The nu(5) Band of (NO)(2) at 26 K

A high-resolution Fourier transform interferometer (Bruker IFS 120 HR) was combined with a uniform supersonic expansion produced by means of axisymmetric Laval nozzles. The geometry profile of the nozzle enabled us to work under precise thermodynamic and kinetic conditions. The effect of the cooling rate of different nozzles on cluster nucleation is illustrated. The experimental sensitivity was tested by recording the nu(5) band of (NO)(2) at 26 K. Copyright 2000 Academic Press.

Effective Rotation-Vibration Parameters for the nu8 and nu4 + nu12 Bands of Ethane

The jet-cooled spectrum of ethane in the region of the nu8 perpendicular fundamental vibration at 1472 cm-1 was recorded with a Fourier transform spectrometer at 0.01 cm-1 instrumental resolution. About 1150 lines were assigned to 18 subbands of nu8 ranging from K"DeltaK = -9 to +8. About 160 lines were assigned to three subbands (K"DeltaK = 0 to +2) of the nu4 + nu12 combination band near 1481 cm-1. Torsional splittings were observed for the majority of the transitions. A stack-by-stack analysis was performed, resulting in effective rovibrational parameters for the upper states nu8 and nu4 + nu12. A number of perturbations was observed and is discussed. Copyright 1999 Academic Press.