Proton spin relaxation in dilute methane gas: A symmetrized theory and its experimental verification

Nuclear spin relaxation in low density methane gas is investigated theoretically and experimentally. A theory is developed in which full account is taken of the tetrahedral symmetry of the molecule. For a nuclear Larmor frequency of 30 MHz, the time evolution of the nonequilibrium magnetization is measured as a function of density between approximately 0.005 and 17 amagats at temperatures of 110, 150, and 295 K. In all cases, exponential relaxation is observed. By using the theory in conjunction with the known spin rotation constants and rotational energy levels of CH4, the measured values of the relaxation rate R1 have been fit very well at each temperature, both for the maximum value of R1 which contains no adjustable parameters and for the density dependence of R1 which contains a single parameter taken to be the collision cross section for molecular reorientation. The centrifugal distortion splittings of the rotational levels are shown to have an important influence on the observed values of R1 at 30 MHz and. more generally on the dependence of the time evolution of the nonequilibrium magnetization on density and frequency. On the basis of the theory, a new type of \u27relaxation rate spectroscopy\u27 is proposed. Non-exponential relaxation is predicted to occur at low densities when the nuclear Larmor frequency is tuned to a centrifugal distortion splitting

Atomic Resonance and Scattering

Contains research objectives.Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 36-039-AMC-03200(E)Sloan Fund for Basic Research (M.I.T. Grant 95

Vampires in the village Žrnovo on the island of Korčula: following an archival document from the 18th century

Središnja tema rada usmjerena je na raščlambu spisa pohranjenog u Državnom arhivu u Mlecima (fond: Capi del Consiglio de’ Dieci: Lettere di Rettori e di altre cariche) koji se odnosi na događaj iz 1748. godine u korčulanskom selu Žrnovo, kada su mještani – vjerujući da su se pojavili vampiri – oskvrnuli nekoliko mjesnih grobova. U radu se podrobno iznose osnovni podaci iz spisa te rečeni događaj analizira u širem društvenom kontekstu i prate se lokalna vjerovanja.The main interest of this essay is the analysis of the document from the State Archive in Venice (file: Capi del Consiglio de’ Dieci: Lettere di Rettori e di altre cariche) which is connected with the episode from 1748 when the inhabitants of the village Žrnove on the island of Korčula in Croatia opened tombs on the local cemetery in the fear of the vampires treating. This essay try to show some social circumstances connected with this event as well as a local vernacular tradition concerning superstitions

NUCLEAR HYPERFINE INTERACTIONS IN SPHERICAL TOPS.

This work was supported in part by the National Science Foundation and the U.S. Office of Naval Research $^{1}$ I. Ozier, L. M. Crapo and S. S. Lee (to be published). $^{2}$ C.H. Anderson and N.F. Ramsey, Phys. Rev. 149, 14 (1966). $^{3}$K. T. Heeht, J. Mol. Spectry, 5, 390 (1960).Author Institution: North American Aviation Science CenterThe problem of nuclear hyperfine interactions in spherical rotors has been solved by the methods of group theory. From this solution, the energy levels for the complete spin-rotation and dipoledipole interactions for a simple tetrahedral molecule have been determined. The frequencies for transitions corresponding to the reorientation of the total spin with respect to a large external magnetic field have been calculated, and the resulting theoretical spectrum has been generated on a high-speed computer. Experimental $data^{1}$ on $CH_{4}, SiH_{4}$ and $GeH_{4}$ have been fitted in terms of this theory, and the corresponding spin rotation constants have been evaluated. The results for $CH_{4}$ agree with the earlier measurements of Anderson and $Ramsey^{2}$, obtained by a different method. The solution of this problem should simplify the analysis of many experiments that involve spherical tops, both in resonance work and in nuclear spin relaxation. This theory also predicts the existence of certain symmetry-breaking transitions between states of different total nuclear spin. These transitions have been observed in methane by means of a level-crossing technique. From the data, it has been possible to measure accurately, for the first time, the centrifugal distortion constant $D_{t}$ in a spherical rotor. $D_{t}=+(140.3 \pm 1.0)kHz.$ This value agrees with Hecht's earlier $estimate^{3}$ of the magnitude of this constant from infrared data. It should be possible with existing experimental techniques, to apply this beam method to many other spherical rotors