Laser magnetic resonance spectrometers

Figure 9.4. Schematic diagram of a far-infrared laser magnetic resonance spectrometer, designed by Evenson [5] and constructed at N.B.S. Boulder.

Several molecules with 3 A. ground states have been studied by both microwave and far-infrared laser magnetic resonance they include O2, SO and SeO. In O2 the observed transitions are necessarily magnetic dipole, and they are frequently used to calibrate the sensitivity of a FIR laser magnetic resonance spectrometer. The other species have electric dipole transitions, and we shall illustrate the situation by describing the studies of SO carried out by Carrington, Levy and Miller [56], SO was also one of the first free radicals to be studied by pure microwave methods, which we will describe in chapter 10. The analysis of the magnetic resonance spectrum actually made use of the parameters determined earlier by pure microwave studies. SO is an easy radical to study experimentally since it is relatively unreactive and has a lifetime of several... 

Far-infrared absorption spectra of H02 in the gas phase have been detected with a water-vapour laser magnetic resonance spectrometer.40 The identification of H02 as the absorbing species is based on a partial analysis of the spectra, and on a variety of different chemical methods used to produce the radical. Using the photochemical 1802 competitive isotopelabelling technique, rate constants have been determined for the reaction of the hydroperoxyl radical with atmospheric sulphur dioxide.41 All measurements were made relative to the disproportionation reaction ... 

A laser magnetic resonance spectrometer has been used in combination with a discharge-flow system to measure the gas-phase reaction rates of the OH radical with NO, NO2 (and CO) at 296 K and over a pressure range 0.4—5 Torr. A study of the behaviour of a number of oxo-nitrogen species in molten NaCl-AlCls mixtures as solvents has been made. The NO ion undergoes reversible one-electron reduction-oxidation at vitreous carbon electrodes. N07 reacts to produce high yields of NO ion, which is separable from the solvent phase as NOCl. NO2, Not, and NOt are reduced to varying extents, whereas N2O and NO remain unaffected for 24 hours. Possible mechanisms for these processes have been discussed. "... 

Clearly the development of experiments involving modem instrumentation is a vibrant part of Physical Chemistry laboratory pedagogy. Equally clearly, there is now a need to focus more strongly on experiments involving instruments other than lasers or magnetic resonance spectrometers. 

The complete set of the three normal vibrations (0-0 stretch), vg (bend), and vg (0-F stretch), has only been observed by IR absorption of the radical isolated in various matrices. In the gas phase, the band center (at 1489 cm" ) was found with a Fourier transform IR spectrometer [2]. Only a small section of the band around 1480 cm" was observed by tuning the Zeeman splittings of vibration-rotation transitions to selected lines of a CO laser (laser magnetic resonance, LMR) [1]. Vg = 579.31839 0.00035 cm (band origin) was measured with a tunable IR diode laser and using Zeeman modulation of absorption lines [3]. 

See also Laser Applications in Electronic Spectroscopy Laser Magnetic Resonance Laser Microprobe Mass Spectrometers Laser Spectroscopy Theory Nonlinear Optical Properties Nonlinear Raman Spectroscopy, Theory X-Ray Spectroscopy, Theory. 

See also EPR, Methods Fluorescence Microscopy, Applications Fluorescent Molecular Probes Hole Burning Spectroscopy, Methods Laser Magnetic Resonance Laser Applications in Electronic Spectroscopy Laser Spectroscopy Theory Light Sources and Optics Luminescence Theory Near-IR Spectrometers Raman Optical Activity, Applications Symmetry in Spectroscopy, Effects of UV-Visible Absorption and Fluorescence Spectrometers Zeeman and Stark Methods in Spectroscopy, Applications. 

Optically-detected magnetic resonance spectroscopy (ODMR) has been used to study the chlorophyll triplet state. Clarke et al.40) utilized an apparatus combining a pair of argon lasers with a microwave spectrometer. Preliminary results are dedicated to determinate structural dynamical features of chlorophyll in vivo. In such experiments the chlorophyll triplet state can be considered as a paramagnetic probe for the surroundings and interactions within the photosynthetic systems40. ... 

Determined by a low angle laser light scattering (LALLS ) device Determined by a H nuclear magnetic resonance (NMR) spectrometer Determined by gel permeation chromatography (GPC) measurement... 

Measurements. The absorption, circular dichroism (CD), and ESR spectra were recorded with a Hitachi 323 spectrophotometer, a JASCO MOE-1 magnetic circular dichroism spectrometer, and a JEOL JES-FE3X ESR spectrometer, respectively. The measurements of the spectra were carried out at 15°-20°C except for the ESR spectra, which were recorded at 77 K. The resonance Raman spectra were recorded at 10°C with 488.0-nm excitation (Ar+ laser) on a JEOL JRS-400D-002 spectrophotometer. The concentration of copper was determined to be 4.9mM by atomic absorption measured by a Nippon Jarrell-Ash AA-1 spectrometer. 

All mass spectra were obtained with a Fourier transform ion cyclotron resonance mass spectrometer (FTMS). The theory and applications of FTMS spectrometry are well-established and will not be discussed here. In our apparatus the sample was located at one of the trap plates of the cell, inside a superconducting magnet. Two pulsed lasers were used, one for tire PFPE desorption and another for metal ion formation. Typically, 2 to 4 mj/pulse of 248 nm or 193-nm light (20 ns fwhm) from an excimer laser was softly focused to an elliptical spot with a 2-mm long axis for desorption. To create the metal ions, a 0.3-mJ pulse of 532-nm light (10 ns fwhm) from the doubled output of a Nd YAG was tightly focused. The metal substrates were prepared from foils of various metals (typically 0.010 in. tiiick). Surface preparation was not critical because the experiment was not sensitive to PFPE/metal surface interactions since the thickness of the polymer films was on the order of 1 pm. 

---