A New Zero‐Field Paramagnetic Resonance Spectrometer
The construction of a new zero‐field paramagnetic resonance (ZFPMR) spectrometer is discussed. Spectrometer organization and construction details are presented for both resonant cavities and broadband traveling‐wave helices as sample holders. A new circuit diagram for a square wave magnetic field modulator with fast rise time is given. The performance of each kind of spectrometer is discussed with particular emphasis on investigation of paramagnetic rare earth ions with zero‐field splittings in diamagnetic host lattices.
Cyclotron resonance and carrier scattering processes in anthracene crystals
Cyclotron resonance experiments on holes orbiting in the ab plane of an anthracene crystal are described in detail. We were unable to reduce the cyclotron resonance experiment to a routine procedure and consequently are able to report useful cyclotron resonance measurements on only a few (six) anthracene crystals. Nevertheless we have been able to obtain useful information on the valence band structure and hole scattering properties in anthracene from these measurements. The measured effective mass of 11 me, where me is the free electron mass, is shown to be in qualitative agreement with calculations of the effective mass tensor. From the shape of the cyclotron resonance line at 2 K, we have obtained experimental hole scattering times ranging from 4×10−10 sec down to 10−12 sec and below depending on sample quality. By a detailed examination of the possible low temperature scattering mechanisms, we have concluded that, at 2 K, holes in anthracene are most efficiently scattered by charges trapped at point d...
The interpretation of optically detected endor in zero field and their relationship to 14N nuclear quadrupole interactions in 3 (ππ*) states of quinoline and quinoxaline
Abstract It is shown that the proper assignment of 14 N ENDOR transitions in azaaromatic π,π * triplet states must take into consideration the contribution of the electron magnetic moment operator to the intensity of a given transition. In quinoline and quinoxaline, the electron magnetic moment operator is found to give the dominant contribution to ENDOR intensities, and to a high degree of accuracy the nuclear moment operator may be neglected. An erroneous ENDOR assignment of quinoxaline is corrected on this basis, and the ENDOR of quinoline is assigned. In particular, we find for these molecules that the dominant ENDOR transitions do not yield the 14 N qudrupole parameters e 2 qQ and η independently, but only the value of 3 e 2 qQ (1-η/3)/4.