Nuclear magnetic spin-rotational relaxation times for linear molecules

The stochastic differential equation study of nuclear magnetic relaxation by spin-rotational interactions is applied to the linear rotator model of the molecule. Inertial effects are included in the calculations, which are performed analytically. Expressions are derived for the spin-rotational contributions to the longitudinal and transverse relaxation times, and for the spin-rotational correlation time.     

Theory of nuclear magnetic spin-rotational relaxation for asymmetric molecules

A stochastic differential equation study of nuclear magnetic relaxation by spin-rotational interactions was successfully completed for spherical, symmetric rotator and linear molecules. This theory has now been extended to asymmetric rotator molecules by first establishing the conditions under which such an extension is mathematically feasible and then investigating the consequences of accepting these conditions.     

A symmetry-based approach to the effective Hamiltonian for symmetric top molecules in degenerate vibronic states

The effective Hamiltonian for a symmetric top molecule in a degenerate vibronic state is obtained. Included in this Hamiltonian are the rotational, spin-rotational, spin-orbit coupling and electronic spin-spin interactions. The terms of the Hamiltonian are expressed as the product of molecular ‘constants,’ rotational angular momentum operators, and symmetry operators. A formalism is derived, and tables included, to determine whether or not a symmetry operator vanishes for a given vibronic state of a particular molecular symmetry. In this way, one can easily obtain all the non-vanishing Hamiltonian terms for a particular application.     

First high-resolution analysis of the 4ν1+ν3 band of nitrogen dioxide near 1.5 μm

The high-resolution absorption spectrum of the 4ν₁+ν₃ band of the ¹⁴N¹⁶O₂ molecule was recorded by CW-Cavity Ring Down Spectroscopy between 6575 and 6700 cm⁻¹. The assignments involve energy levels of the (4,0,1) vibrational state with rotational quantum numbers up to K_a=8 and N=48. A large majority of the spin-rotation energy levels were reproduced within their experimental uncertainty using a theoretical model which takes explicitly into account the Coriolis interactions between the spin-rotational levels of the (4,0,1) vibrational state and those of the (4,2,0) and of (0,9,0) dark states, the anharmonic interactions between the (4,2,0) and (0,9,0) states together with the electron spin-rotation resonances within the (4,0,1), (4,2,0) and (0,9,0) states. Precise vibrational energies, rotational, spin-rotational, and coupling constants were determined for the {(4,2,0), (0,9,0), (4,0,1)} triad of interacting states. Using these parameters and the value of the transition dipole-moment operator determined from a fit of a selection of experimental line intensities, the synthetic spectrum of the 4ν₁+ν₃ band was generated and is provided as Supplementary Material.     

Vibrational,rotational, and isotopic dependence of CaBr X2Σ spin-rotational and HFS parameters

The previously published molecular-beam, laser-rf, double-resonance study of the rotational and isotopic dependences of the spin-rotational and hyperfine interactions in the v″ = 0, X²Σ state of CaBr is supplemented here with data for v″ = 1. The vibrational dependence of the parameters is now obtained. The results for CaBr are displayed along with analogous, previously published results for CaF and CaCl.     

Nuclear magnetic spin-lattice relaxation and molecular motion in solid white phosphorus and in liquid phosphorus

The ³¹P spin-lattice relaxation rates have been measured in solid white phosphorus and in liquid phosphorus over the temperature range 110 K to 400 K and at Larmor frequencies of 10 MHz and 30 MHz. The contributions to the measured relaxation rate from the different interactions have been separated. In the low-temperature, crystalline phase there are important contributions to the relaxation rate from the anisotropic chemical shielding and the intramolecular dipole-dipole interactions which are modulated by the reorientational motion of the molecule. Interference effects between these two interactions, which are important in liquids, are demonstrated to be quenched by the strong dipolar interactions in the solid. The reorientational correlation time is given by

and the chemical shielding anisotropy by

In the high-temperature, plastic-crystalline phase the reorientational correlation time is

as obtained from the anisotropic chemical shielding relaxation rate which is separated from the other contributions by its quadratic dependence on the Larmor frequency. Using this τ _R the intramolecular dipole-dipole relaxation rate is calculated. The contribution from the translational diffusion modulated intermolecular dipole-dipole interaction is calculated from the self-diffusion coefficient. When these contributions are subtracted from the observed relaxation rate, there remains a frequency-independent relaxation rate, proportional to 1/δ _R , which is attributed to the spin-rotational interaction. The latter is shown to be quantitatively consistent with large-angle reorientational jumps of the P₄ molecules by 120° about their C _3v axes. The relaxation in the liquid phase is dominated by the spin-rotational interaction and the expression representing the spin-rotational relaxation rate is the same as the one derived in the plastic-crystalline phase. The mechanism of molecular reorientation in the liquid is therefore the same as in the plastic-crystalline phase.     

Electron resonance spectra of some radicals derived from acetylenes and nitriles

The electron resonance spectra of a series of radicals derived by hydrogen abstraction from substrates containing carbon-carbon or carbon-nitrogen triple bonds have been studied in fluid solutions. The radicals ·CH₂CN, ·CH₂C ≡ CH and ·CH₂C ≡ C·CH₃ which have a linear heavy-atom framework show interesting temperature dependent line-width variations. These are attributed to spin-rotational interactions arising from anisotropic molecular reorientation. It is suggested that the motion about the long axis of these radicals is inertial in character.

The equilibrium geometries and hyperfine coupling constants of the propargyl and cyanomethyl radicals have been estimated from INDO-LCAO-SCF calculations.     

转动传能中NH2()精细结构态变化的研究

利用高分辨光谱技术他NH2（A~2A1,090)423(F1/F2) 在单次碰撞条件下的精细态色散光光谱,发现NH2（A~2A1)在与团壳层分子碰撞传能过程中,母能级的自旋－转动耦合守恒,从实验上直接证实了在开壳层－ 壳层分子碰撞过程中电子自旋为一旁观者的假设;由于长程作用力造成子能级有保持原来自旋－转动耦合的倾向。     

Laser flash photolysis and time-resolved CIDNP study of photochemical reactions between aqueous tryptophan and nucleotides

The theory of deuteron spin-lattice relaxation for free D₂ quantum rotors is developed. Relaxation rates are calculated forortho-D₂ andpara-D₂. The spin-rotational interaction as well as quadrupole and dipole-dipole interactions under interference condition are taken into account. Relaxation rates, to be compared with experiment, are derived as weighted sums of contributions from different rotational states according to their Boltzmann populations. The theory is applied to explain relaxation rates measured in a wide temperature range for D₂ molecules in NaY zeolite cages. At high temperatures (above 110 K), a scattering of molecules on the cage walls provides the relaxation mechanism. At low temperatures, molecules stay close to the surface and undergo reorientations in a potential introduced by the adsorption centers.     

Topological Majorana and Dirac zero modes in superconducting vortex cores

We provide an argument based on flux insertion to show that certain superconductors with a nontrivial topological invariant have protected zero modes in their vortex cores. This argument has the flavor of a two-dimensional index theorem and applies to disordered systems as well. It also provides a new way of understanding the zero modes in the vortex cores of a spinless px+ipy superconductor. Applying this approach to superconductors with and without time-reversal and spin-rotational symmetry, we predict the necessary and sufficient conditions for protected zero modes to exist in their vortices.     

First detection of a muonated organic free radical in the gas phase

We report the observation of the muonated ethyl radical in transverse magnetic fields. The radical is possibly formed by addition of epithermal Mu to ethylene. The pressure dependence of the line widths is discussed in terms of relaxation mechanisms of dipolar and spin-rotational origin.     

Microwave spectrum of 15N16O2 in the ground state

¹⁵NO₂ (88 lines) in the ground state has been observed in the microwave spectral region up to 170 GHz. The least squares analysis gave the higher order distortion terms of rotational and spin-rotational Hamiltonian.     

First high-resolution analysis of the 5ν3 band of nitrogen dioxide near 1.3 μm

The first high-resolution absorption spectrum of the 5ν₃ band of the ¹⁴N¹⁶O₂ molecule at 7766.071 cm^?1 was recorded by high sensitivity CW-Cavity Ring Down Spectroscopy between 7674 and 7795 cm^?1. The noise equivalent absorption of the recordings was α_min≈1×10^?10 cm^?1. The assignments involve energy levels of the (0,0,5) vibrational state with rotational quantum numbers up to K_a=9 and N=47. The set of the spin–rotation energy levels were reproduced within their experimental uncertainty using a theoretical model, which takes explicitly into account the Coriolis interactions between the spin rotational levels of the (0,0,5) vibrational state and those of the (0,2,4) dark state together with the electron spin–rotation resonances within the (0,0,5) and (0,2,4) states. Precise values were determined for the (0,0,5) vibrational energy rotational, spin-rotational constants and for the (0,2,4)?(0,0,5) coupling constants. In addition the (0,2,4) rotational and spin-rotational constants were estimated. Using these parameters and the value of the transition dipole moment operator determined from a fit of a selection of experimental line intensities, the synthetic spectrum of the 5ν₃ band was generated and is provided as Supplementary material.     

The far-infrared laser magnetic resonance spectrum of the CH radical

Transitions between the spin-rotational levels of the ¹³CH radical in the v=0 level of the ground state have been detected by the technique of laser magnetic resonance at far-infrared wavelengths. These measurements have been combined with the previous measurements of the lambda-doubling intervals of the molecule [J. Chem. Phys. 85 (1986) 1276 ] to determine an improved set of molecular parameters for ¹³CH. The analysis provides accurate predictions of the transition frequencies between the low-lying spin-rotational levels of the radical at zero magnetic field. A comparison is made with the values of the corresponding parameters of ¹²CH which reveals small effects due to the breakdown of the Born-Oppenheimer approximation.     

Universal conductance fluctuations in Sierpinski carpets

We theoretically investigate the conductance fluctuation of two-terminal device in Sierpinski carpets. We find that, for the circular orthogonal ensemble (COE), the conductance fluctuation does not display a universal feature; but for circular unitary ensemble (CUE) without time-reversal symmetry or circular symplectic ensemble (CSE) without spin-rotational symmetry, the conductance fluctuation can reach an identical universal value of 0.74±0.01(e²/h). We further find that the conductance distributions around the critical disorder strength for both CUE and CSE systems share the similar distribution forms. Our findings provide a better understanding of the electronic transport properties of the regular fractal structure.     

Rashba billiards

We study the energy levels of non-interacting electrons confined to move in two-dimensional billiard regions and having a spin-dependent dynamics due to a finite Rashba spin splitting. The free space Green's function for such Rashba billiards is constructed analytically and used to find the area and perimeter contributions to the density of states, as well as the corresponding smooth counting function. We show that, in contrast to systems with spin-rotational invariance, Rashba billiards always possess a negative energy spectrum. A semi-classical analysis is presented to interpret the singular behavior of the density of states at certain negative energies for circular Rashba billiards. Our detailed analysis of the spin structure of circular Rashba billiards reveals a finite out-of-plane spin projection for electron eigenstates.     

Spin splittings in the ν3 band of NO2

Spin splittings for several important atmospheric lines in the ν₃ band of NO₂ have been measured by diode laser. An improved spin-splitting program has been developed which takes into account the asymmetry effects in the lower K_a splittings. The measured spin splittings and the derived spin-rotational constants are reported in this study to a much higher accuracy than previously achieved.     

Part of the far-infrared laser magnetic resonance spectrum of the HF free radical

Transitions between the spin-rotational levels of the HF⁺ radical in the v=0 level of the X²Π ground state have been observed by the technique of laser magnetic resonance at far-infrared wavelengths. Because of the large spin-orbit coupling in this ²Π state, the detection of the fine-structure transitions required the use of very short-wavelength laser lines (down to 40 μm). These observations have provided accurate information on the ¹⁹F hyperfine splittings in rotational levels of the upper spin component for the first time which has enabled the complete determination of the hyperfine structure for this molecule. An effective Hamiltonian was used to model the experimental measurements; this provided considerably more accurate values for the various molecular parameters than previously available. Using these parameters, predictions of the transition frequencies between the low-lying spin-rotational levels of the radical at zero magnetic field have been made.     

Cooper pairs with broken parity and spin-rotational symmetries in d-wave superconductors

Paramagnetic effects are shown to result in the appearance of a triplet component of order parameter in a vortex phase of a -wave superconductor in the absence of impurities. This component, which breaks parity and spin-rotational symmetries of Cooper pairs, is expected to be of the order of unity in a number of modern superconductors such as organic, high Tc, and some others. A generic phase diagram of such type-IV superconductors, which are singlet ones at H=0 and in the Meissner phase, and characterized by singlet-triplet mixed Copper pairs Deltas+iDeltat with broken symmetries in a vortex phase, is discussed.