Laser microwave spectroscopy solids

This chapter assesses the state of the art in laser microwave spectroscopy, i.e., investigations where both laser radiation and microwave radiation are involved. The many concepts and methods applied to numerous different atomic, molecular, and solid state systems are outlined, not always with emphasis on completeness of all the later references to the same method. This chapter hopefully stimulates further development of laser microwave spectroscopic methods and applications, even crossing the border of different disciplines. 

Combined laser-microwave spectroscopy based on optical pumping was also performed in the solid state. Spectral line broadening caused, e.g., by strain and phonon interaction, can be overcome by extreme cooling and specific site selective procedures. Very narrow lines are attainable particularly in the spectra of rare earth ions doped to crystals in low concentration. Rare earth ions, therefore, play an important role in solid state spectroscopy, as will be illustrated in the course of this section. 

Since the turn of the present century, a series of linear complexes with the general formula NgMX (Ng = Ar, Kr, Xe M = Cu, Ag, Au X = F, Cl, Br) have been prepared and characterized by physical methods. These complexes were prepared by laser ablation of the metal from its solid and letting the resulting plasma react with the appropriate precursor. The complexes formed were then stabilized in a supersonic jet of argon gas. Characterization of these complexes was carried out mainly by microwave spectroscopy. 

The seminal work of Marcus and Hush has had a significant impact on the development of PET. Pioneering efforts by Sutin, Hopfield, Jortner, and others established the connection between thermal electron transfer and photoelectron transfer [6]. This work set the stage for a notable series of experiments where laser flash spectroscopy [7], chemically induced nuclear polarization [8], resonance Raman spectroscopy [9], time-resolved microwave conductivity [10], and time-resolved photoacoustic calorimetry [11], to site only a few examples, have been successfully employed to chart the dynamics of PET in homogeneous solution, the solid-state, and organized assemblies. 

Example 5.7 Figure 5.13 gives an example of microwave spectroscopy in an excited vibrational state, where the (A Ka,Kc = 1,2) rotational level in the excited vibrational state V2 = I of DCCCHO has been selectively populated by infrared pumping with a HeXe laser [535]. The solid arrows represent the direct microwave transitions from the pumped level, while the wavy arrows correspond to triple-resonance transitions starting from levels that have been populated either by the first microwave quantum or by collision-induced transitions from the laser-pumped level. 

Similar to 2DR, ribose (C5H5O5) is one of the most important monosaccharides since it constitutes a subunit of the backbone of RNA. NMR studies have shown that ribose in solution is a mixture of a- and p-pyranose and a- and p-furanose forms, the p-pyranose form being predominant. The recently settled crystal structures have shown that the a- and P-pyranose forms are present in the solid phase [239-243]. The structure in the gas phase has been experimentally investigated using a laser ablation molecular beam Fourier transform microwave spectroscopy (LA-MBFTMW) technique [62]. The high resolution rotational spectrum has provided structural information on a total of six rotamers of ribose, three belonging to the a-pyranose forms and other three to the P-pyranose forms. Recently, D-ribose (m.p. 95°C) has been submitted to a laser ablation broadband (CP-FTMW) spectroscopic study and eight conformers (two new a-pyranose forms) have been identified. A broadband section of the spectra is shown in Fig. 35 and the detected conformers depicted in Fig. 36. 

Sources. The ultimate source for spectroscopic studies is one that is intense and monochromatic but tunable, so that no dispersion device is needed. Microwave sonrces such as klystrons and Gnnn diodes meet these requirements for rotational spectroscopy, and lasers can be similarly nsed for selected regions in the infrared and for much of the visible-ultraviolet regions. In the 500 to 4000 cm infrared region, solid-state diode and F-center lasers allow scans over 50 to 300 cm regions at very high resolution (<0.001 cm ), but these sources are still quite expensive and nontrival to operate. This is less trne... 

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... 

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