Heteronuclear double resonance studies of trisilylphosphine and trisilylstibine

The relative signs of all the coupling constants involving ¹H, ²⁹Si and ³¹P in (²⁸SiH₃)₂P²⁹SiH₃ and (²⁸SiH₃)₂Sb²⁹SiH₃ have been determined by ¹H-{²⁹Si} and ¹H-{³¹P} ‘tickling’ experiments. With the exception of ¹ K(²⁹Si-³¹P), the reduced coupling constants are probably positive over one and three bonds, and negative over two and four bonds.     

Heteronuclear double resonance on formamide-15N and ammonium-15N using weak perturbing radiofrequency fields

Weak radiofrequency fields have been used to perturb nitrogen transitions in the formamide-¹⁵N and ammonium-¹⁵N molecules. Observation of the proton spectra has completed the determination of the relative signs of the coupling constants in formamide-¹⁵N. Chemical shifts precisely related to tetramethylsilane are reported and a discussion of a method for presentation of shift results is included.     

Heteronuclear intermolecular single-quantum coherences in liquid nuclear magnetic resonance

This paper analyses the heteronuclear Cosy Revamped by Asymmetric Z-gradient Echo Detection pulse sequence. General theoretical expressions of the pulse sequence with arbitrary flip angles were derived by using dipolar field treatment and signals originating from heteronuclear intermolecular single-quantum coherences （iSQCs） in highly-polarized two spin-1/2 systems were mainly discussed in order to find the optimal flip angles. The results show that signals from heteronuclear iSQCs decay slower than those from intermolecular double-quantum coherences or intermolecular zero-quantum coherences. Magical angle experiments validate that the signals are from heteronuclear iSQCs and insensitive to the imperfection of radio-frequency flip angles. All experimental observations are in excellent agreement with theoretical predictions. The quantum-mechanical treatment leads to similar predictions to the dipolar field treatment.     

Heteronuclear dipolar decoupling in solid-state nuclear magnetic resonance under ultra-high magic-angle spinning

We compare in this communication several heteronuclear dipolar decoupling sequences in solid-state nuclear magnetic resonance experiments under a magic-angle spinning frequency of 60 kHz. The decoupling radiofrequency field amplitudes considered are 190 and 10 kHz. No substantial difference was found among the sequences considered here in performance barring the difference in the optimisation protocol of the various schemes, an aspect that favours the use of swept-frequency two pulse phase modulation (SW(f)-TPPM).     

A study of stochastic resonance in a bistable system with double stochasticity

In a simple stochastic system—an overdamped Kramers oscillator with two noise sources (sources of white and dichotomic noise)—stochastic resonance is investigated theoretically and by means of analog simulation as a function of the asymmetry of the potential and the amplitude and the correlation time of the dichotomic noise. It is found that stochastic resonance is observed under slow (compared with the Kramers switching time) dichotomic noise and the signal-to-noise ratio (SNR) has a maximum for a noise amplitude equal to static bias.     

Specific MARY spectrum from radical anion of pentafluorobenzene

The paper presents the first resolved experimental magnetically affected reaction yield (MARY) spectrum for a system with nonequivalent nuclei, radical anion of pentafluorobenzene. This observation dispels the common apprehension that because of a rather involved energy level layout a system with not all nuclei magnetically equivalent cannot produce resolved MARY lines in nonzero fields, and greatly, increases the practical scope of level-crossing techniques for studies of spin-correlated radical pairs. The experimental finding is supported by schemes of energy levels calculated for this system.     

Double-quantum filtered rotational-echo double resonance

The homonuclear scalar coupling of a directly bonded 13C-13C pair has been used to create a double-quantum filter (DQF) to remove the natural-abundance 13C background in 13C{15N} rotational-echo double-resonance (REDOR) experiments. The DQF scalar and REDOR dipolar evolution periods are coincident which is important for sensitivity in the event of weak 13C-15N dipolar coupling. Calculated and observed 13C{15N} DQF-REDOR dephasings were in agreement for a test sample of mixed recrystallized labeled alanines. Glycine metabolism in a single uniform-15N soybean leaf labeled for 6 min by 13CO2 was measured quantitatively by 13C{15N} DQF-REDOR with no background interferences.     

Microwave spectrum and dipole moment of pentafluorobenzene

With the idea of evaluating the dipole moment of pentafluorobenzene from a lowJ transition, its microwave spectrum was investigated in the frequency region of 8,000 to 12,400 MHz. The spectrum had been earlier observed by the authors in the 12,400 to 18,000 MHz region which needs reassignment in the light of present investigations. The rotational constants areA=1480·856±0·003 MHz,B=1030·066±0·003 MHz andC=607·496±0·002 MHz. The dipole moment is 1·44±0·05 D.     

Autler-Townes effect in double optical resonance

Two frequency stabilized dye lasers and a sodium atomic beam are used to study the Autler-Townes effect in the aligned 3S_{$\text{1}\text{2}$}, F = 2, $\text{M}{}_{\mathrm{F}}\text{= 2 → 3P}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$, F = 3, M_F = 3, → 4D_{$\text{5}\text{2}$}, F = 4, M_F = 4 states. This system is to a very good approximation an isolated three-level atom. The Autler-Townes doublet splittings are measured as a function of the intensities of the two lasers and their detunings from resonance. The experimental results are in good agreement with theory.     

Interaction-enhanced double resonance in cold gases

A new type of double-resonance spectroscopy of a quantum gas based on interaction-induced frequency modulation of a probe transition has been considered. Interstate interaction of multilevel atoms causes a coherence-dependent collisional shift of the transition between the atomic states |1〉 and |2〉 due to a nonzero population of the state |3〉. Thus, the frequency of the probe transition |1〉?|2〉 experiences oscillations associated with the Rabi oscillations between the states |1〉 and |3〉 under continuous excitation of the drive resonance |1〉?|3〉. Such a dynamic frequency shift leads to a change in the electromagnetic absorption at the probe frequency and, consequently, greatly enhances the sensitivity of double-resonance spectroscopy as compared to traditional “hole burning”, which is solely due to a decrease in the population of the initial state |1〉. In particular, it has been shown that the resonance linewidth is determined by the magnitude of the contact shift and the amplitude of the drive field and does not depend on the static field gradient. The calculated line shape and width agree with the low-temperature electron-nuclear double-resonance spectra of two-dimensional atomic hydrogen.     

Fast beam collinear laser-rf double resonance

The method and application of fast beam collinear laser-rf double resonance are discussed. Following a short theoretical treatment of the collinear interaction of fast atoms with rf and laser fields, the experimental procedure and some technical details are presented. Selected applications of the method: (i) hyperfine structure and atomicg-factor measurements, and (ii) experimental studies of fundamental aspects of atom-field interactions, are described. prospective applications in nuclear physics experiments are discussed.     

Matrix signals in electron-electron double resonance

The ΔM_{I= 0}, ELDOR spectra of nitroxide radicals in amorphous polystyrene and polypropylene matrices display absorptions at Δv = 13.5 and 27 MHz. The intensities of these signals are decreased by about 35 % in perdeuterated polystyrene. This and the frequency establishes the signals to be matrix ELDOR which results when nonbonded protons interact with the resultant of the external field and the electronic field. The 〈α_eβ′_H∥↔∥β_eα″_H〉 forbidden transition then becomes allowed. Rapid-passage results are also consistent with this model.     

Magnetic double resonance in force microscopy

Magnetic-resonance force microscopy is combined with cross-polarization and spin-decoupling NMR techniques to obtain double-resonance NMR signals of micrometer-scaled objects. The effective one-dimensional spatial resolution obtained in our experiments performed on a KPF6 single crystal sample is approximately 0.5 microm. The spectral linewidth of 900 Hz is sample limited. The described double-resonance techniques can introduce new chemical specificity to the magnetic-force sensor.     

Nonstationary nutations in heteronuclear double resonance

It is shown that in any coupled heteronuclear system, nonstationary perturbation of some nuclei leads, under certain conditions, to nutation oscillations of the components of the magnetizations of the other nuclei. The nature of these nutations is determined by the relaxation parameters of both subsystems and the conditions under which they are excited.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 15–19, February, 1979.     

Cooperative effects in optical double resonance

A theory of optical double resonance which takes into account the cooperative interactions among atoms is formulated. The analytical result for the double resonance spectra in the conventional situation when the probe field is weak, is given. The changes in the nature of the spectra as one sweeps from cooperative to single atom branch are discussed. The cooperative interaction is shown to reduce considerably the asymmetry of the Autler-Towne's doublet.