F. Geoffrey Herring

Perturbation corrections to Koopmans' theorem. II. A study of basis set variation

Ordinary third‐order Rayleigh Schrodinger perturbation theory is used to evaluate vertical ionization potentials of closed‐shell molecules. The variation in the accuracy of the method as the size of the basis set increases is investigated for water. From this study, the smallest basis compatible with reasonable accuracy is selected as the best compromise between cost and accuracy. This basis is used to calculate the vertical ionization potentials of H2O, CH2, NH3, H2CO, F2O, and CO. The results are compared to those obtained from a double‐zeta basis set.

A theoretical study of the vertical ionization potentials of HNO, FNO, O3, CF2 and N2H2

Abstract The vertical ionization potentials of HNO, FNO, O 3 , CF 2 and N 2 H 2 have been calculated using Rayleigh—Schrodinger Perturbation Theory

Dispersion versus absorption (DISPA): Modulation broadening and instrumental distortions in electron paramagnetic resonance lineshapes

Abstract Plots of dispersion versus absorption (DISPA) in NMR have previously been shown to provide an extremely sensitive test for deviations from Lorentzian lineshape. In this paper, the experimental absorption derivative EPR spectrum of peroxylamine disulfonate (PADS) is digitized during field-sweep detection and numerically integrated to give an absorption spectrum, which is then numerically Hilbert transformed to yield a dispersion spectrum, and in turn a DISPA plot. The effect of field modulation is demonstrated both theoretically and experimentally to produce an EPR DISPA curve whose displacement outside its reference circle is directly related to the strength of the modulating field. The modulating field strength can thus be determined without external calibration, using a single DISPA plot. In addition, DISPA detection of small lineshape distortions resulting from field sweep at rates faster than are appropriate to the time constant of the phase-sensitive detector is demonstrated experimentally. Finally, the circular DISPA plot for PADS at high concentration readily illustrates the homogeneous nature of the line broadening, again from a single EPR spectrum. These results show that the DISPA technique can be used, even when only the absorption spectrum is experimentally available.