Double Resonance Spectra Research Articles

Conformation and Photodissociation Process of Benzo-15-Crown-5 and Benzo-18-Crown-6 Complexes with Ammonium Ions Investigated by Cold UV and IR Spectroscopy in the Gas Phase.

We examined the conformation of benzo-15-crown-5 (B15C5) and benzo-18-crown-6 (B18C6) complexes with ammonium ions, NH4+, CH3NH3+ (MeNH3+), CH3CH2NH3+ (EtNH3+), and CH3CH2CH2NH3+ (PrNH3+), using cold UV and IR spectroscopy in the gas phase. We measured the UV photodissociation (UVPD) spectra of the ammonium complexes and compared them with those of the K+(B15C5) and K+(B18C6) complexes in order to identify the conformation on the basis of the band position. The number of possible conformations for the ammonium complexes of B15C5 is limited compared with alkali metal ions with similar ionic radii. The NH4+(B15C5), MeNH3+(B15C5), and EtNH3+(B15C5) complexes show two conformers, whereas the K+(B15C5) complex has three stable conformers. In the case of the PrNH3+(B15C5) complex, one conformer was found predominantly in the UVPD spectrum. The ammonium complexes of B15C5 prefer to adopt crown conformations with large dihedral angles on the C-O-C-C atoms around the benzene moiety. In the case of the ammonium complexes of B18C6, two or three conformers were found in the UVPD spectra. One conformation of the B18C6 complexes is similar to that of the K+(B18C6) complex, which has a planar form on the C-O-C-C atoms around the benzene moiety. The other but dominant conformations of the ammonium complexes could be attributed to those with large C-O-C-C dihedral angles. These conformational findings for the ammonium complexes suggest that the benzo-crown ethers tend to adopt nonplanar conformations around the benzene moiety to encapsulate the ammonium ions. The IR-UV double-resonance (DR) spectra of the B15C5 and B18C6 complexes were compared to those of benzo-12-crown-4 (B12C4) and dibenzo-18-crown-6 (DB18C6) complexes. The N-H···O hydrogen bond (H-bond) is weaker with increasing ring size from B12C4 to B18C6, although the calculated binding energy is smaller for B12C4 than for B18C6. This result indicates that cooperative H-bonds with three N-H groups can strengthen the intermolecular bond between the ammonium ions and B18C6. The difference in the conformational preference between the ammonium and K+ complexes is attributed to directed N-H···O H-bonds in the ammonium complexes. Proton transfer and dissociation of the crown ring were also observed for the photoexcitation of the NH4+(B15C5) and NH4+(B18C6) complexes.

Double Hanle resonance dependence on light polarization angle and transverse magnetic field direction

We present experimental and theoretical investigations of the dependence of double Hanle resonance spectrum on the light polarization angle and the direction of the applied transverse magnetic field (TMF). The experiments are done for Fg=2→Fe=1 transition of 87Rb D1 line using a rubidium vapor cell containing buffer gas. We show that a small light polarization component along the direction of TMF introduces asymmetry in the double Hanle resonance signal. Both the magnitude and sign of asymmetry in the signal are sensitive to the TMF orientation, suggesting a possible method for in-situ measurement of the direction of the magnetic fields generated by the coils. The physical origin of this asymmetry is explained by considering the redistribution of population among the ground-state Zeeman sublevels in the presence of TMF. In addition, we systematically vary both the polarization angle and TMF direction to study their effect on the line profile of Hanle resonances. We demonstrate that a double Hanle resonance changes to a dark Hanle resonance by rotating the light polarization vector irrespective of the TMF direction. We have developed a simple theoretical model based on a degenerate two-level system to explain our experimental observations.

Deep-Ultraviolet and Helicity-Dependent Raman Spectroscopy for Carbon Nanotubes and 2D Materials.

Recent progress of Raman spectroscopy on carbon nanotubes and 2D materials is reviewed as a topical review. The Raman tensor with complex values is related to the chiral 1D/2D materials without mirror symmetry for the mirror in the propagating direction of light, such as chiral carbon nanotube and black phosphorus. The phenomenon of complex Raman tensor is observed by the asymmetric polar plot of helicity-dependent Raman spectroscopy using incident circularly-polarized lights. First-principles calculations of resonant Raman spectra directly give the complex Raman tensor that explains helicity-dependent Raman spectra and laser-energy-dependent relative intensities of Raman spectra. In deep-ultraviolet (DUV) Raman spectroscopy with 266 nm laser, since the energy of the photon is large compared with the energy gap, the first-order and double resonant Raman processes occur in general k points in the Brillouin zone. First-principles calculation is necessary to understand the DUV Raman spectra and the origin of double-resonance Raman spectra. Asymmetric line shapes appear for the G band of graphene for 266 nm laser and in-plane Raman mode of WS2 for 532 nm laser, while these spectra show symmetric line shapes for other laser excitation. The interference effect on the asymmetric line shape is discussed by fitting the spectra to the Breit-Wigner-Fano lineshapes.

Theory of infrared double-resonance Raman spectrum in graphene: The role of the zone-boundary electron-phonon enhancement

Theory of infrared double-resonance Raman spectrum in graphene: The role of the zone-boundary electron-phonon enhancement

Double-Resonance Spectroscopy of Coupled Electron Spins on a Surface.

Scanning-tunneling microscopy (STM) combined with electron spin resonance (ESR) has enabled single-spin spectroscopy with nanoelectronvolt energy resolution and angstrom-scale spatial resolution, which allows quantum sensing and magnetic resonance imaging at the atomic scale. Extending this spectroscopic tool to a study of multiple spins, however, is nontrivial due to the extreme locality of the STM tunnel junction. Here we demonstrate double electron-electron spin resonance spectroscopy in an STM for two coupled atomic spins by simultaneously and independently driving them using two continuous-wave radio frequency voltages. We show the ability to drive and detect the resonance of a spin that is remote from the tunnel junction while read-out is achieved via the spin in the tunnel junction. Open quantum system simulations for two coupled spins reproduce all double-resonance spectra and further reveal a relaxation time of the remote spin that is longer by an order of magnitude than that of the local spin in the tunnel junction. Our technique can be applied to quantum-coherent multi-spin sensing, simulation, and manipulation in engineered spin structures on surfaces.

Normal and anomalous dispersion study on probe light propagation in the presence of structured coupling light using electromagnetically induced transparency protocol

Here, we present a study on the dispersion features obtained in an electromagnetically induced transparency (EIT) experiment using a three-level cascade configuration in an 87Rb atomic vapor medium in the presence of Laguerre–Gaussian (LG) light as a coupling. A doublet transmission structure was obtained experimentally, and dispersion spectra were extracted using transmission spectra to study the probe light behavior. Dispersive regions that exhibit normal and anomalous nature were studied considering the polarization of various orientations as a coupling light. We established that normal dispersive region shows steep positive slopes, and anomalous dispersive region shows negative slopes, which can be controlled by polarization orientations. Owing to the change in the slopes of dispersion, normal and anomalous dispersive region is observed, and spectrum shows the effects of subluminal and superluminal propagation of probe light. This work, to the best of our knowledge, is novel in the study of dispersive region arising out of double-resonance EIT transmission spectra in the presence of LG light with the l=10 and p=0 mode as a coupling light with various polarization orientations. In the discussion, we establish that single parameter θ is sufficient for identifying the orientation and ellipticity of the polarization ellipse and also determine that the polarization of coupling light acts as a tuning parameter for changing the behavior of normal and anomalous dispersive region. Slow and fast light or superluminal propagation of probe light arise as a consequence of positive or negative group index, and fast light does not violate the principle of causality. Slow and fast light have future applications in high-speed quantum information and quantum communication using EIT-based protocol.

Cryogenic Ion Spectroscopy of Protonated and Sodiated Methyladenine Derivatives.

Ultraviolet photodissociation (UVPD) spectra of protonated 9-methyladenine (H+9MA), protonated 7-methyl adenine (H+7MA), protonated 3-methyladenine (H+3MA), and sodiated 7-methyladenine (Na+7MA) near the origin bands of the S0-S1 transition were obtained using cryogenic ion spectroscopy. The UV-UV hole burning, infrared (IR) ion-dip, and IR-UV double resonance spectra showed that all the ions were present as single isomers in a cryogenic ion trap. The UVPD spectrum of H+9MA exhibited only a broad absorption band, whereas the spectra of H+7MA, H+3MA, and Na+7MA displayed moderately or well-resolved vibronic bands. Potential energy profiles were computed to understand the reason for the different bandwidths of the vibronic bands in the spectra. The broadening of the bands was correlated with the slopes between the Franck-Condon point and the conical intersection between the S1 and S0 states in the potential energy profiles, thus reflecting the deactivation rates in the S1 state.

Conformation of Benzo-12-Crown-4 Complexes with Ammonium Ions Investigated by Cold Gas-Phase Spectroscopy.

In this study, we examined the conformation and intermolecular interactions of benzo-12-crown-4 (B12C4) complexes with NH4+, CH3NH3+ (MeNH3+), CH3CH2NH3+ (EtNH3+), and CH3CH2CH2NH3+ (PrNH3+) using cold gas-phase spectroscopy. All of the B12C4 complexes showed sharp vibronic features in the UV photodissociation spectra, and the position of the 0-0 band was close to that of the B12C4 complex with an isotropic K+ guest. This result suggests that the conformation of B12C4 is maintained despite oriented interactions with ammonium guests via anisotropic N-H···O interactions. Further, we measured the IR-UV double-resonance spectra of these complexes in the NH stretching region. In the IR-UV spectra of the EtNH3+ and PrNH3+ complexes, two distinct IR fingerprints were observed depending on the UV probe wavelength selected, indicating the existence of another (second) conformer for these complexes. Quantum chemical calculations clarified that the second conformer of the EtNH3+ and PrNH3+ complexes was partially stabilized by the C-H···π hydrogen bond. The conformation of B12C4 complexes with ammonium ions is strongly affected by the interaction between the alkyl chain of the ion guest and the benzene ring of the B12C4 host, although the main intermolecular interaction occurs between the NH3+ group and crown cavity through the N-H···O hydrogen bonds.

Spectroscopic Study of the B 1Π State of NaH.

In this study, the B1Π excited state of NaH has been experimentally studied for the first time. Pulsed laser-induced fluorescence excitation spectroscopy was used to investigate the B1Π electronic state of NaH. A total of 48 ro-vibronic transitions were observed, including within the B–X (0–0) and B–X (0–1) transition bands. Only one B-state vibrational level was identified, and a series of PQR lines, with eight e-parity and eight f-parity sublevels (v′ = 0, J′ = 1–8), were assigned. The level assignment was supported by a comparison of the experimental line positions with the ab initio calculations, the dispersed laser-induced fluorescence spectrum of the NaH B1Π → X1∑+ emission, and the V-type optical–optical double resonance spectra. The Dunham-type coefficients, the mean internuclear distance, the harmonic vibrational frequency ω, and the dissociation energies D0 and De of the B1Π state were determined.

Microwave Magnetic Field Pattern Evaluation of Horn and Patch Antennas Using Cs Atomic Sensor

In this study, microwave (9.2 GHz) magnetic field radiation patterns of a horn antenna in the near-field (10 cm) and of a patch antenna in the near-field (3 mm, 2 cm) and far-field (10 cm) are measured using a Cs atomic sensor with $7\pi $ and $8~\sigma $ Zeeman double radio optical resonance (DROR) spectra at 6S1/2(F = 3, $\text{m}_{f}$ ) – 6S1/2 (F = 4, $\text{m}_{f}$ ) - 6P3/2(F = 4) transition by applying a 6 Gauss external magnetic field. Radiation patterns of a horn antenna and a patch antenna are characterized by measuring the DROR amplitude, while rotating the antennas 360 degrees relative to the atomic sensor, and the results are compared to patterns measured in the anechoic chamber using traditional methods. Radiation patterns in both polarizations are measured in a single full rotation, by measuring the $\pi $ and $\sigma $ Zeeman DROR fluorescence amplitudes at the same time. In addition, near-field microwave magnetic field radiation patterns of the patch antenna at orthogonal polarizations are measured at 3 mm distance by moving the antenna ±12.5 mm on the horizontal plane. Advantages and possible applications of small-sized atomic sensors in radiation pattern measurements at different polarizations and radiation analysis of complicated emitters such as circuit boards are discussed.

Crossover from a Solid Effect to Thermal Mixing 1H Dynamic Nuclear Polarization with Trityl-OX063.

Trityl-OX063 is a narrow-line, water-soluble, and biocompatible polarizing agent, widely used for dynamic nuclear polarization (DNP) amplified NMR of 13C, but not of the abundant 1H nuclear spin, for which the ineffective solid effect (SE) is expected to be operational. Surprisingly, we observed a crossover from SE to thermal mixing (TM) DNP of 1H with increasing Trityl-OX063 concentration at 7 T. We experimentally ascertained diagnostic signatures of TM-DNP that have only been theoretically predicted: (i) an electron paramagnetic resonance (EPR) spectrum that maintains an asymmetrically broadened EPR line from strong e-e couplings and (ii) hyperpolarization, i.e., cooling of select electron-spin populations, manifested in a characteristic pump-probe electron double-resonance spectrum under DNP conditions. Low microwave power requirements, high polarization transfer rates, and efficient DNP at high magnetic fields are the key benefits of TM-DNP.

Induced Fit of Crown Cavity to Ammonium Ion Guests and Photoinduced Intracavity Reactions: Cold Gas-Phase Spectroscopy of Dibenzo-18-Crown-6 Complexes with NH4+, CH3NH3+, and CH3CH2NH3.

Ultraviolet photodissociation (UVPD) spectra of dibenzo-18-crown-6 (DB18C6) complexes with NH4+, CH3NH3+ (MeNH3+), and CH3CH2NH3+ (EtNH3+) [NH4+(DB18C6), MeNH3+(DB18C6), and EtNH3+(DB18C6), respectively] were observed under cold gas-phase conditions. We also measured the infrared (IR)-UV double-resonance spectra of these complexes in the NH stretching region to examine the encapsulation structure. The UVPD and IR-UV spectra were analyzed using quantum chemical calculations. All the ammonium complexes show sharp 0-0 bands at positions close to that of the K+(DB18C6) complex; the conformation of the DB18C6 component in the ammonium complexes is similar to that in K+(DB18C6). In addition, the ammonium complexes each have another type of isomer that the K+(DB18C6) complex does not show in the gas phase. In these isomers, the conformation of the DB18C6 cavity changes, and the strength of the NH···O hydrogen bond increases. During the UVPD, the NH4+(DB18C6) complex provides various photofragment species, such as the C8H9O2+ ion, resulting from cleavage of the DB18C6 component, whereas the dominant fragment ion for the MeNH3+(DB18C6) and EtNH3+(DB18C6) complexes is the ammonium ion itself. The UVPD investigation of deuterated systems suggests that after UV excitation of the NH4+(DB18C6) complex, the dissociation process is initiated by proton transfer from NH4+ to DB18C6, followed by the migration of hydrogen atoms in the crown cavity and the cleavage of the ether ring.

Spectroscopic Signatures of Mode-Dependent Tunnel Splitting in the Iodide-Water Binary Complex.

The gas-phase vibrational spectrum of the isolated iodide-water cluster ion (I-·H2O), first reported in 1996, presents one of the most difficult, long-standing spectroscopic puzzles involving ion microhydration. Although the spectra of the smaller halides are well described in the context of an asymmetrical ground-state structure in which only one OH group is hydrogen-bonded to the ion, the I-·H2O spectrum displays multiplet structures with partially resolved rotational patterns that are additionally influenced by quantum nuclear spin statistics. In this study, this complex behavior is unraveled with a combination of experimental methods, including ion preparation in a temperature-controlled ion trap and spectral simplification through applications of tag-free, two-color IR-IR double-resonance spectroscopy. Analysis of the double-resonance spectra reveals a vibrational ground-state tunneling splitting of about 20 cm-1, which is on the same order as the spacing between the peaks that comprise the multiplet structure. These findings are further supported by the results obtained from a fully coupled, six-dimensional calculation of the vibrational spectrum. The underlying level structure can then be understood as a consequence of experimentally measurable, vibrational mode-dependent tunneling splittings (which, in the case of the ground vibrational state, is comparable to the rotational energy spacing between levels with Ka = 0 and 1), as well as Fermi resonance interactions. The latter include the hydrogen-bonded OH stretches and combination bands that involve the HOH bend overtones and soft-mode excitations of frustrated translation and rotation displacements of the water molecule relative to the ion. These anharmonic couplings yield closely spaced bands that are activated in the IR by borrowing intensity from the OH stretch fundamentals.

Enhancement of Photoluminescence and Raman Scattering in Hybrid Thin-Film Structures of a-C:H with Silver Nanoparticles

The changes occurring in the optical density, photoluminescence (PL), and Raman scattering (RS) spectra of thin-film structures based on a-C:H and granulated silver films after annealing of samples at 200°C are studied. A hypsochromic shift of the main plasmon peak, formation of double resonance spectra, and an increase in band intensities were observed after annealing of samples with a 10-nm gravimetric thickness of the Ag film. It is shown that both the Ag film nanostructure morphology and the a-C:H film electronic structure affect the plasmon enhancement of PL and Raman spectra. A more efficient PL enhancement was observed after annealing of samples based on a-C:H with optical band gap Eg = 0.4 eV. At the same time, the initially higher PL intensity of samples with Eg = 2.7 eV almost did not change. The enhancement of resonance RS had a selective character. It was related to scattering by polycyclic aromatic groups, which are dominant in the structure of the a-C:H film with a narrower optical band gap.

Усиление фотолюминесценции и комбинационного рассеяния в гибридных тонкопленочных структурах a-C:H с наночастицами серебра

n this work, we studied changes in the spectra of optical density, photoluminescence (PL) and Raman spectra of hybrid thin-film structures based on a-C: H and granular silver films before and after annealing of samples at 200 ° C. The hypsochromic shift of the main plasmon peak, the formation of double resonance spectra, and an increase in the band intensity were observed after annealing of samples with the gravimetric Ag film thickness of 10 nm. The influence of both the morphology of the nanostructure of Ag films and the features of the electronic structure of a-C: H films were observed on the plasmon enhancement of the PL and Raman spectra. For samples based on a-C:H with an optical gap Eg = 0.4 eV, a more effective PL enhancement was observed after annealing of the samples. At the same time, in the samples with Eg = 2.7 eV, the PL intensity practically did not change, remaining higher. The amplification of resonant Raman scattering was selective. It was associated with scattering by polycyclic aromatic groups predominant in the structure of the a-C: H film with a narrower optical gap.

Double plasmon resonance in hybrid structures of silver nanoparticles with amorphous hydrogenated carbon

ABSTRACTIn this work, double plasmon resonances in hybrid structures comprising Ag nanoparticles (NPs) and amorphous hydrogenated carbon films (a-C:H) have been studied. Granulated silver films with a gravimetric thickness of 10 nm were thermally deposited on top or underneath a-C:H films fabricated by plasma-assisted chemical vapour deposition on a quartz substrate. Two plasmon bands with comparable intensities have been observed in the hybrid structures optical density spectrum after annealing at 200°C. On the other hand, in the absence of the amorphous hydrogenated carbon film the short-wavelength peak in the optical density spectrum of the same Ag film is hardly observable. In addition, plasmon-enhanced photoluminescence of the a-C:H film being excited close to the spectral dip at the wavelength of 405 nm was observed. The nature of double plasmon resonance spectra were discussed and explained by the resonance interaction of plasmons excited in Ag NPs with excitons in a-C:H.

The binuclear cluster of [FeFe] hydrogenase is formed with sulfur donated by cysteine of an [Fe(Cys)(CO)2(CN)] organometallic precursor

The enzyme [FeFe]-hydrogenase (HydA1) contains a unique 6-iron cofactor, the H-cluster, that has unusual ligands to an Fe-Fe binuclear subcluster: CN-, CO, and an azadithiolate (adt) ligand that provides 2 S bridges between the 2 Fe atoms. In cells, the H-cluster is assembled by a collection of 3 maturases: HydE and HydF, whose roles aren't fully understood, and HydG, which has been shown to construct a [Fe(Cys)(CO)2(CN)] organometallic precursor to the binuclear cluster. Here, we report the in vitro assembly of the H-cluster in the absence of HydG, which is functionally replaced by adding a synthetic [Fe(Cys)(CO)2(CN)] carrier in the maturation reaction. The synthetic carrier and the HydG-generated analog exhibit similar infrared spectra. The carrier allows HydG-free maturation to HydA1, whose activity matches that of the native enzyme. Maturation with 13CN-containing carrier affords 13CN-labeled enzyme as verified by electron paramagnetic resonance (EPR)/electron nuclear double-resonance spectra. This synthetic surrogate approach complements existing biochemical strategies and greatly facilitates the understanding of pathways involved in the assembly of the H-cluster. As an immediate demonstration, we clarify that Cys is not the source of the carbon and nitrogen atoms in the adt ligand using pulse EPR to target the magnetic couplings introduced via a 13C3,15N-Cys-labeled synthetic carrier. Parallel mass-spectrometry experiments show that the Cys backbone is converted to pyruvate, consistent with a cysteine role in donating S in forming the adt bridge. This mechanistic scenario is confirmed via maturation with a seleno-Cys carrier to form HydA1-Se, where the incorporation of Se was characterized by extended X-ray absorption fine structure spectroscopy.

Bandwidth analysis of AC magnetic field sensing based on electronic spin double-resonance of nitrogen-vacancy centers in diamond

We have recently demonstrated an AC magnetic field sensing scheme using a simple continuous-wave optically detected magnetic resonance of nitrogen-vacancy centers in diamond. This scheme is based on electronic spin double-resonance excited by continuous microwave and radiofrequency (RF) fields. Here, we measure and analyze the double-resonance spectrum and magnetic field sensitivity for various microwave and RF frequencies. We observe a clear anticrossing of RF-dressed electronic spin states in the spectrum and estimate the bandwidth to be approximately 5 MHz at a center frequency of 9.9 MHz.

Flavodoxin with an air-stable flavin semiquinone in a green sulfur bacterium.

Flavodoxins are small proteins with a non-covalently bound FMN that can accept two electrons and accordingly adopt three redox states: oxidized (quinone), one-electron reduced (semiquinone), and two-electron reduced (quinol). In iron-deficient cyanobacteria and algae, flavodoxin can substitute for ferredoxin as the electron carrier in the photosynthetic electron transport chain. Here, we demonstrate a similar function for flavodoxin from the green sulfur bacterium Chlorobium phaeovibrioides (cp-Fld). The expression of the cp-Fld gene, found in a close proximity with the genes for other proteins associated with iron transport and storage, increased in a low-iron medium. cp-Fld produced in Escherichia coli exhibited the optical, ERP, and electron-nuclear double resonance spectra that were similar to those of known flavodoxins. However, unlike all other flavodoxins, cp-Fld exhibited unprecedented stability of FMN semiquinone to oxidation by air and difference in midpoint redox potentials for the quinone-semiquinone and semiquinone-quinol couples (- 110 and - 530mV, respectively). cp-Fld could be reduced by pyruvate:ferredoxin oxidoreductase found in the membrane-free extract of Chl. phaeovibrioides cells and photo-reduced by the photosynthetic reaction center found in membrane vesicles from these cells. The green sulfur bacterium Chl. phaeovibrioides appears thus to be a new type of the photosynthetic organisms that can use flavodoxin as an alternative electron carrier to cope with iron deficiency.

95 GHz electron paramagnetic resonance of LiYF4: Nd3+ crystal in parallel orientation

We report the observation of the conventional and pulsed electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR) spectra from 19F and 7Li nuclei on impurity Nd3+ ions in LiYF4 crystal doped with Nd3+ ions in parallel orientation at microwave frequency of ν ≈ 95 GHz (W-band). The resolved structure from the nearby and remote nuclei in spectra is observed. The outcome shows that LiYF4:Nd3+ system can be exploited as a convenient matrix for performing spin manipulations and adjusting quantum computation protocols while ENDOR technique is usable for the investigation of electron-nuclear interaction with the nuclei of the system.