Microwave optical double resonance spectroscopy

R.W. Field, A.D. English, T. Tanaka, D.O. Harris, P.A. Jennings Microwave optical double resonance spectroscopy with a cw dye laser ... 

An important development in microwave/optical double resonance, called microwave/optical polarisation spectroscopy, was described by Ernst and Torring [42], The principles of this technique are illustrated in figure 11.22. A linearly polarised probe beam from a tunable laser is sent through the gas sample and a nearly crossed linear polariser, before its final detection. Polarised microwave radiation resonant with a rotational transition in the gas sample is introduced via a microwave horn as shown, and resonant absorption results in a partial change in polarisation of... 

Radford (1961, 1962) and Radford and Broida (1962) presented a complete theory of the Zeeman effect for diatomic molecules that included perturbation effects. This led to a series of detailed investigations of the CN B2E+ (v — 0) A2II (v = 10) perturbation in which many of the techniques of modern high-resolution molecular spectroscopy and analysis were first demonstrated anticrossing spectroscopy (Radford and Broida, 1962, 1963), microwave optical double resonance (Evenson, et at, 1964), excited-state hyperfine structure with perturbations (Radford, 1964), effect of perturbations on radiative lifetimes and on inter-electronic-state collisional energy transfer (Radford and Broida, 1963). A similarly complete treatment of the effect of a magnetic field on the CO a,3E+ A1 perturbation complex is reported by Sykora and Vidal (1998). The AS = 0 selection rule for the Zeeman Hamiltonian leads to important differences between the CN B2E+ A2II and CO a/3E+ A1 perturbation plus Zeeman examples, primarily in the absence in the latter case of interference effects between the Zeeman and intramolecular perturbation terms. 

Millimeter wave spectroscopy with a free space cell such as a Broida oven is more sensitive than lower frequency microwave spectroscopy. However, the higher J transitions monitored by millimeter wave spectroscopy often do not show the effects of hyperfine structure. In the case of CaOH and SrOH, the proton hyperfine structure was measured in beautiful pump-probe microwave optical double resonance experiments in the Steimle group [24,68], They adapted the classic atomic beam magnetic resonance experiments to work with a pulsed laser vaporization source and replaced the microwave fields in the A and C regions by optical fields (Fig. 15). These sensitive, high-precision measurements yielded a very small value for the proton Fermi contact parameter (bF), consistent with ionic bonding and a... 

Electron-impact Spectra.—A review of electron-scattering spectroscopy has appeared.265 Electron-impact spectra have been reported of helium,263 H and He,267 Li,258 Ba,259 Hg,280 H2,261 CO,282 Rbl and KI,283 NO and N20,284 water,286 ammonia and methane,2866 N02,288 and C02.287 The study on NOa yields the interesting result that the 2B2 state is asymmetric, possessing different equilibrium bond lengths between the N atom and each atom this can explain the results of recent microwave-optical double-resonance experiments.288... 

Double-resonance Spectroscopy.—A review has been given of double-resonance methods in spectroscopy.378 Attention will be focused here on optically (usually phosphorescence) detected magnetic resonance experiments (ODMR). Microwave-optical double-resonance experiments have been carried out on the spectrum of gaseous N02,379 permitting assignment of the rotational = 0—4 side-bands of the 493 nm band. 

Microwave-Optical Double-Resonance Polarization Spectroscopy... 

A very sensitive and accurate double-resonance technique is microwave-optical double-resonance polarization spectroscopy (MOPS), developed by Ernst et al. 

Mode 2 is a particularly sensitive method to detect mw transitions as will be shown in chapter III and is called microwave-optical polarization spectroscopy (MOPS). Polarization spectroscopy techniques require less intensity of laser and mw radiation than the corresponding nonlinear methods based on fluorescence detection. Power broadening is avoided which is the reason for the largely improved resolution of MOPS compared to conventional microwave optical double resonance (MOOR) spec-... 

There are many experimental techniques for the determination of the Spin-Hamiltonian parameters g, Ux, J. D, E. Often applied are Electron Paramagnetic or Spin Resonance (EPR, ESR), Electron Nuclear Double Resonance (ENDOR) or Triple Resonance, Electron-Electron Double Resonance (ELDOR), Nuclear Magnetic Resonance (NMR), occasionally utilizing effects of Chemically Induced Dynamic Nuclear Polarization (CIDNP), Optical Detections of Magnetic Resonance (ODMR) or Microwave Optical Double Resonance (MODR), Laser Magnetic Resonance (LMR), Atomic Beam Spectroscopy, and Muon Spin Rotation (/iSR). The extraction of data from the spectra varies with the methods, the system studied and the physical state of the sample (gas, liquid, unordered or ordered solid). For these procedures the reader is referred to the monographs (D). Further, effective magnetic moments of free radicals are often obtained from static... 

Meth. MW MB IR MODR method of measurement used in the given reference corresponding to the preceding quoted values microwave spectroscopy molecular beam resonance experiment-electric or magnetic resonance infrared with lasers microwave optical double resonance... 

Meth. DR LA LM MB MW RA method of measurement applied to obtain the reported value double resonance experiments (microwave-optical double resonance MODR or radiofrequency-optical double resonance RFDR) Doppler free laser spectrosefipy laser magnetic resonance molecular beam electric resonance or molecular beam resonance with laser detection method microwave spectroscopy radio astronomy... 

A new very sensitive and accurate double-resonance technique is the Microwave-Optical double-resonance Polarization Spectroscopy (MOPS) developed by Ernst et. al [10.93]. This technique detects microwave transitions in a sample between crossed polarizers through the change in transmission of a polarized optical wave. The sensitivity of the method has been demonstrated by measurements of the hfs of rotational transitions in the electronic ground state of CaCl molecules which were produced by the reaction 2Ca+ CI2 - CaCl in an argon flow. In spite of the small concentrations of CaCl reaction products and the short absorption pathlength in the reaction zone a good signal-to-noise ratio could be achieved at linewidths of lf2 MHz [10.94]. 

Spectroscopy utilizing tunable laser and microwave sources has been applied widely in exploring atoms, molecules, and condensed matter. Besides the classical areas of optical double resonance and optical pumping the extension of these or related methods to difference frequency measurements in the optical range seems to be of increasing importance. This includes heterodyne techniques. Laser microwave schemes can also play an essential role for the generation of modem frequen( standards. Last but not least, there will be many technical applications like infrared detectors, wavemeters, magnetometers, etc. 

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