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  • 1
    Electronic Resource
    Electronic Resource
    Endor [electron-nuclear double resonance] of methyl, matrix, and .alpha. protons in amorphous and polycrystalline matrixes (1968)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 72 (1968), S. 4269-4276 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100858a056
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  • 2
    Electronic Resource
    Electronic Resource
    Elevation of copper nuclear quadrupole coupling in thio complexes by completion of the coordination sphere (1983)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 87 (1983), S. 2509-2512 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100237a014
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  • 3
    Electronic Resource
    Electronic Resource
    E.P.R. OBSERVATION OF NH3+ FORMED BY X-RAY IRRADIATION OF AMMONIUM PERCHLORATE CRYSTALS (1961)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 65 (1961), S. 1636-1638 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100905a508
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  • 4
    Electronic Resource
    Electronic Resource
    Continuous wave multi-quantum electron paramagnetic resonance spectroscopy (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 3891-3898 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The equation of Anderson [Phys. Rev. 102, 151 (1956)] (ω2−ω1)2=(γH0−ω1)2+γ2H21, which describes resonance conditions if relaxation times are long and irradiation at two frequencies is applied to a spin system, has been studied experimentally in the context of continuous wave electron paramagnetic resonance (EPR) spectroscopy. Here ω2 and ω1 are the frequencies of two incident microwave levels, one of which is much stronger than the other and is of amplitude H1. γH0 is the resonant condition if just one frequency is applied. Magnetization at either ω1 or ω2 has been observed as a function of sweep of the static magnetic field, sweep of ω2 and also sweep of the amplitude H1. Observation of magnetization at frequency ω1 corresponding to the strong microwave field H1 replicates the rotary saturation experiment of Redfield [Phys. Rev. 98, 1787 (1955)]. Multi-quantum effects are studied with the two frequencies well separated and also when they lie within the width of a single homogeneous line. In addition, data are shown when both microwave amplitudes are similar and the Anderson equation is no longer correct. The thrust of the work is not only to study the spin physics, but also to develop a basis for our development of rotary resonance as an alternative to field modulation in EPR spectroscopy [J. Chem. Soc. Faraday Trans. 1 85, 3901 (1989)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458775
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  • 5
    Electronic Resource
    Electronic Resource
    Use of high observing power in electron spin resonance saturation-recovery experiments in spin-labeled membranes (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 6029-6035 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Biomolecular collision rates of 14N-containing nitroxide radical labeled stearic acid with similar 15N-containing species in dimyristoylphosphatidylcholine (DMPC) liposomes have been determined using the saturation-recovery electron spin resonance (ESR) method. It is shown that high microwave observing powers can be used to obtain these rates, thereby increasing the signal-to-noise ratio by about ten times relative to methods previously used. The data are analyzed using the rate-equation approach with inclusion of the observing transition probability. A number of solutions to these equations for other experimental situations and for pulse and continuous wave electron–electron double resonance (ELDOR) are also presented. The bimolecular collision rate of labels at the C16 position was found to be 20% greater than for labels at the C12 position, suggesting that the interaction distance differs at these two positions. Even though the high observing power does not affect the ability to extract bimolecular collision rates, the effective spin-lattice relaxation rates are altered. Plots of these latter rates versus power are linear and the slope can be used to determine the absolute microwave field at the sample for a given input power.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457420
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  • 6
    Electronic Resource
    Electronic Resource
    Continuous wave multiquantum electron paramagnetic resonance spectroscopy. II. Spin-system generated intermodulation sidebands (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 5907-5916 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Irradiation of a single homogeneous electron paramagnetic resonance (EPR) transition by two microwave sources separated by Δf, where Δf(very-much-less-than) the linewidth, results in the production of intermodulation sidebands at f0±(k+1/2)Δf, where f0 is the mean of the two irradiating frequencies and k is an integer ≥1. These sidebands can be seen directly with a microwave spectrum analyzer. Any one of the sidebands can be observed by suitable phase sensitive detection and displayed as a function of the polarizing magnetic field H0, resulting in a multiquantum EPR spectrum. The widths of the EPR lines decrease as k increases, resulting in improved resolution. The two k=1 transitions can be superimposed, resulting in a signal of double intensity. At saturating microwave power, this double-intensity line is two times less intense than an ordinary EPR line. No magnetic field modulation needs to be used when detecting multiquantum transitions, and pure absorption or pure dispersion signals are obtained with good baseline stability. Considerable attention is paid to the technical problem of irradiating the sample with just two microwave frequencies. In the apparatus described, spurious instrumental sidebands are reduced by 60 dB or more.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460451
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  • 7
    Electronic Resource
    Electronic Resource
    Continuous wave multiquantum electron paramagnetic resonance spectroscopy. III. Theory of intermodulation sidebands (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 1786-1796 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The interaction of a spin 1/2 system with two continuous wave transverse electromagnetic fields is studied using the dressed-atom formalism and the Floquet theory. The equation of motion of the density matrix in the presence of two fields is solved and used to analyze the response of the spin system to double irradiation under steady state. In the average frequency rotating frame, the diagonal elements of the density matrix oscillate at even harmonics of the frequency difference, while the off-diagonal elements oscillate at odd harmonics. The spectral response of the spin system can be predicted by applying the conservation rules: The frequency spectrum is a consequence of the conservation of total angular momentum, while the resonance condition is the result of the conservation of energy. The interpretive and predictive nature of the theoretical framework presented is illustrated by the treatment of the classical Anderson experiment and the simulation of the splitting of the multiquantum signal at high frequency difference. Approximate expressions for the population differences and coherences are derived and graphic representation is used to study the general nonlinear dependence on spectral parameters. At low values of the saturation parameter S, the n-quantum absorption is proportional to dT2S(n−1)/2, where d=1/2γH. Therefore, the signal amplitude is proportional not only to T2, but also to powers of T1T2, which makes the multiquantum signals more sensitive to relaxation rates than conventional one-photon displays. The frequency difference swept line shape of the multiquantum signal depends on both T1 and T2. However, when T2(very-much-less-than)T1, the new spectroscopic dimension, namely, the frequency difference, can be used to determine the spin–lattice relaxation time. Several spectroscopic features of multiquantum signals are discussed in the context of the general mathematical equivalence of double irradiation and amplitude modulation spectroscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464267
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  • 8
    Electronic Resource
    Electronic Resource
    Continuous wave multiquantum electron paramagnetic resonance spectroscopy. IV. Multiquantum electron–nuclear double resonance (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 4975-4985 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report a theoretical and experimental investigation of the interaction of a coupled electron–nuclear spin system with three electromagnetic fields: two equally intense microwave fields resonant with the electron spin, and one radio-frequency field resonant with the nuclear spin. This is an electron–nuclear double-resonance experiment where the effect of the nuclear transition is detected via changes of the electron multiple photon transitions (MQ-EPR) rather than steady-state saturation and, therefore, is called multiquantum electron–nuclear double resonance (MQ-ENDOR). The theoretical framework previously developed for the description of multiple photon phenomena in a two level system is extended to the case of a four level system. The equation of motion of the density matrix is solved in the presence of three fields, which results in five master equations relating various populations and coherences. A ten photon approximation is used to study the functional dependence on spectral parameters and determine the sensitivity of this technique to spin relaxation rates. The experimental investigation is carried out on a sample of tri-t-butyl phenoxyl radical dissolved in mineral oil. At low values of the electron saturation factor Se, the rf-swept MQ-ENDOR is a de-enhancement of the 3Q-EPR signal (i.e., the first intermodulation sidebands). As the microwave field strength increases, the MQ-ENDOR signal changes phase by 180° due to dominance of generalized saturation. Higher order MQ-EPR signals (i.e., higher order sidebands) have larger negative enhancement and tend to display smaller positive enhancement. Line splitting results if the microwave frequency difference or field strength is increased. The dependence of MQ-ENDOR displays on various spectral parameters was found to be consistent with the general trends predicted by the theory. These displays provide a convenient way to estimate electron and nuclear relaxation rates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465999
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  • 9
    Electronic Resource
    Electronic Resource
    X-band low phase noise Gunn diode oscillator for EPR spectroscopy (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4010-4011 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Two low phase-noise Gunn diode X-band oscillators intended for use in electron paramagnetic resonance (EPR) spectroscopy are described. In the first, a 250-mW MA49159 Gunn diode oscillator (M/A-COM, Burlington, MA) is mounted in a coaxial transmission line that is closely coupled to a TE011 transmission cavity that in turn is loosely coupled to the output transmission line. The output power is 50 mW and the phase noise is −145 dBc/Hz at 100 kHz offset. In the second, two such coaxial assemblies are used with 500-mW MA49110 diodes for increased power. The output power is 150 mW and the phase noise is −150 dBc/Hz at 100-kHz offset. These phase noise values are in the range of 24–29 dB better than the specification for a normal high quality klystron used in commercial spectrometers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143257
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  • 10
    Electronic Resource
    Electronic Resource
    Electron paramagnetic resonance detection by time-locked subsampling (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 2622-2628 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A detection method for electron paramagnetic resonance spectroscopy is described that permits simultaneous acquisition of multiple in- and out-of-phase harmonics of the response to magnetic-field modulation for both dispersion and absorption: (i) conversion of the microwave carrier to an intermediate frequency (IF) carrier; (ii) subsampling of the IF carrier by an analog-to-digital converter four times in K IF cycles where K is an odd integer; (iii) dividing the digital words into two streams, odd indexes in one and even in the other, followed by sign inversion of every other word in each stream; and (iv) feeding the two streams to a computer for the digital equivalent of phase-sensitive detection (PSD). The system is broadbanded, in the frequency domain, with narrow banding for improved signal-to-noise ratio occurring only at the PSD step. All gains and phases are internally consistent. The method is demonstrated for a nitroxide spin label. A fundamental improvement is achieved by collecting more information than is possible using a single analog PSD. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148989
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