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Rotational spectra have been observed for four isotopes of ArHBr and ArDBr and eight isotopes of KrHBr and KrDBr using a Fabry–Perot Fourier transform spectrometer with a pulsed supersonic nozzle as the molecular source. The rotational constants in the ground vibrational state ?0 with their centrifugal distortions DJ, as well as Br nuclear quadrupole coupling constants χa, are given. In addition, an important centrifugal distortion of the Br quadrupole coupling constant, Dχ, an indicator of the coupling between the radial and angular potentials, is given for ArHBr and KrHBr. The Br spin–rotation interaction c in ArHBr is also obtained. The results are: The molecular structures are consistent with a linear equilibrium geometry with the H(D) atom located between Br and the rare gas atoms. The complexes undergo large amplitude vibrations and estimates of the bending and stretching force constants and frequencies are given. By combining the bending, stretching, and their coupling, we have obtained the harmonic bending and stretching force constants (ks1 and kb1) and 6/12 Lennard-Jones potential parameters (ε and Re) for ArHCl, KrHCl, ArHBr, KrHBr.

A semiclassical theory has been developed to describe pulsed Fourier transform microwave spectroscopy carried out in a Fabry–Perot cavity. A density matrix formalism is used to study the interaction of a two-level quantum system with a classical standing wave electric field, appropriate for the Fabry–Perot cavity. Equations describing the polarization of, and subsequent emission of radiation by arbitrary distributions of molecules in the cavity are derived. The specific problem of a static Maxwell–Boltzmann gas is studied in detail, both theoretically and experimentally. The static gas line shape in the power-broadened limit is described by an ordinary Doppler and pressure broadened envelope. Sensitivities of the ordinary waveguide cell and Fabry–Perot cavity pulsed Fourier transform spectrometers using static gas samples are compared.

The gas dynamics of a pulsed supersonic nozzle molecular source are investigated by using a pulsed Fabry–Perot cavity microwave spectrometer to obtain free induction decay signals from rotational two-level systems in the gas expansion. An equation is derived giving the time domain emission signal line shape as an integral over the active molecular distribution in the beam. The Doppler splitting phenomenon is discussed in detail. Experimental line shapes are deconvoluted to give molecular velocities, dephasing times, and density distributions. We find that the density distribution of active molecules from the the pulsed nozzle varies rapidly in time, starting with a depletion on the nozzle axis at short times after the nozzle is opened, and changing to on-axis concentration at longer times. Results obtained with the gas nozzle axis oriented at angles ranging from 0 ° to 90 ° with respect to the direction of propagation of the microwaves are reported.

Photoelectron spectrum of the XeHCl van der Waals molecule J. Chem. Phys. 94, 4680 (1991); 10.1063/1.460601The rotational spectra, molecular structures, and 2 0 1Hg nuclear quadrupole coupling constants of HgHCl and HgDCl J. Chem. Phys. 81, 5326 (1984); 10.1063/1.447675Microwave and radio frequency spectrum of XeHCl Rotational spectra have been assigned for the 129XeH"Cl, 129XeH37C1, 129XeD"Cl, IlIXeH"CI and I "XeH'''CI van der Waals molecules by employing pulsed microwave Fourier transform spectroscopy in a Fabry-Perot cavity with a pulsed supersonic nozzle as the molecular source. The rotational constants, centrifugal distortion constants, and Cl nuclear quadrupole coupling constants obtained from the spectra are used to determine the structure of XeHCl and to gain information on the intermolecular potential binding of Xe to HC!. From the spectrum of IlIXeH"CI and an analysis of the centrifugal distortion in 129XeH"Cl, 11IXeH.I'CI, and 132XeH"CI the 13IXe nuclear quadrupole coupling constant in XeHCI is found to be -4.9±0.2 MHz. Using the known nuclear quadrupole moment of 13IXe, the electric field gradient at the Xe nucleus is calculated. The observed field gradient is discussed in terms of Sternheimer shielding and formation of the weak Xe-HCl van der Waals bond.The analysiS of the spectrum of 131XeH35CI was greatly