Analysis Of Isotope Shifts Research Articles

Coupling Isotopic Shifts with Collision Cross-Section Measurements for Carbohydrate Characterization in High-Resolution Ion Mobility Separations.

Herein, we introduce a two-dimensional strategy to better characterize carbohydrate isomers. In a single experiment, we can derive cyclic ion mobility-mass spectrometry (cIMS-MS)-based collision cross-section (CCS) values in conjunction with measuring isotopic shifts through the relative arrival times of light and heavy isotopologues. These isotopic shifts were introduced by permethylating carbohydrates with either light, CH3, or heavy, CD3, labels at every available hydroxyl group to generate a light/heavy pair of isotopologues for every individual species analyzed. We observed that our calculated CCS values, which were exclusively measured for the light isotopologues, were orthogonal to our measured isotopic shifts (i.e., relative arrival time values between heavy and light permethylated isotopologues). Our permethylation-induced isotopic shifts scaled well with increasing molecular weight, up to ∼m/z 1300, expanding the analysis of isotopic shifts to molecules 3-4 times as large as those previously studied. Our presented use of coupling CCS values with the measurement of isotopic shifts in a single cIMS-MS experiment is a proof-of-concept demonstration that our two-dimensional approach can improve the characterization of challenging isomeric carbohydrates. We envision that our presented 2D approach will have broad utility for varying molecular classes as well as being amenable to many forms of derivatization.

Non-Empirical Analysis of Isotopic Shifts and Resonance Effects in the Infrared High-Resolution Spectrum of Freon-22 (CHF2Cl), Enriched with 13C

Non-Empirical Analysis of Isotopic Shifts and Resonance Effects in the Infrared High-Resolution Spectrum of Freon-22 (CHF2Cl), Enriched with 13C

King-Plot Analysis of Isotope Shifts in Simple Diatomic Molecules

We demonstrate that the isotope shift in isotopomers of diatomic molecules, where the nucleus of one of its constituent atoms is replaced by another isotope, can be expressed as the sum of a field shift and a mass shift, similar to the atomic case. We show that a linear relation holds between atomic and molecular isotopes shifts, thus extending the King-plot analysis to molecular isotope shifts. Optical isotope shifts in YbF and ZrO and infrared isotope shifts in SnH are analyzed with a molecular King-plot approach, utilizing Yb$^{+}$ and Zr$^{+}$ ionic isotope shifts and charge radii of Sn obtained with non-optical methods. The changes in the mean-squared nuclear charge radii $\delta \langle r^2 \rangle$ of $^{170-174,176}$Yb and $^{90-92,94,96}$Zr extracted from the molecular transitions are found to be in excellent agreement with the values from the spectroscopy of Yb$^{+}$ and Zr$^{+}$, respectively. On the contrary, in the case of the vibrational-rotational transition in SnH, no sensitivity to the nuclear volume could be deduced within the experimental resolution, which makes it unsuitable for the extraction of nuclear charge radii but provides insights into the molecular electronic wave function not accessible via other methods. The new opportunities offered by the molecular King-plot analysis for research in nuclear structure and molecular physics are discussed.

Normal mode analysis of isotopic shifts in Raman spectrum of TNT-d5

A combined experimental-computational study was conducted on the Raman spectrum of TNT-d5 in the present study. It was found that among the 24 hybrid density functional theory (DFT) methods, O3LYP, tHCTHhyb, and B3LYP simulations yielded the strongest Raman bands which were closest to those measured from experiments. Simulations of hybrid DFT methods did not show that deuterium replacements alter orientations of 2- and 6-nitro with respect to phenyl ring, considering a larger size of the methyl group. However, the deuterium replacements apparently changed the reduced masses for all deuterium related vibrations. Although no difference of structural parameters was shown between TNT and its deuterated analogue, discrepancy was indicated in vibrational zero energy from our simulations. O3LYP simulation exhibited 24 deuterium involved vibrations, which were coupled into seven Raman bands of TNT-d5. This phenomenon can account for the experimental Raman band shifts or split of TNT-d5 when compared with the corresponding bands of TNT. The present study and its outcomes provide in-depth microchemical insights of Raman characteristics of TNT and may facilitate the design of nano-structures of SERS substrates for detection of TNT and its degradation products. All intensities displayed in this study were calculated from numerical simulations.

Zeeman-hyperfine structures and isotope effect in the spectrum of Tl I

The Zeeman structures of seventeen lines of 205Tl I (Z=81) covering the UV-NIR spectral range (351.92–1151.28) nm were investigated. Landé gJ-factors for eighteen levels were determined for the first time. Furthermore, we have performed fine structure studies for both even- and odd-configuration levels and determined the relevant parameters. For the 6s6p2 configuration we have refined the suggested level energies and predicted positions for missing levels. With regard to hyperfine structure (hfs), we have justified the surprisingly huge value of the magnetic hfs constant A(6s210s). Moreover, we have extracted the single-electron hfs constant parameter values for the lowest even-parity configurations of 205Tl I; for instance a10s10(6s210s)=1015(9)MHz and a6s10(6s6p2)=217306(205)MHz. Regarding isotope shift analysis we have observed that Dirac–Fock calculations, preferably chosen to take into account the contribution of the p1/2 contact-electron, are in good agreement with experimental data for low-lying levels of each configuration under study.

Structure and dynamics of the electronically excited C 1 and D 0+ states of ArXe from high-resolution vacuum ultraviolet spectra

Vacuum ultraviolet spectra of the C 1 ← X 0(+) and D 0(+) ← X 0(+) band systems of ArXe have been recorded at high resolution. Analysis of the rotational structure of the spectra of several isotopomers, and in the case of Ar(129)Xe and Ar(131)Xe also of the hyperfine structure, has led to the derivation of a complete set of spectroscopic parameters for the C 1 and D 0(+) states. The rovibrational energy level structure of the C 1 state reveals strong homogeneous perturbations with neighboring Ω = 1 electronic states. The analysis of isotopic shifts led to a reassignment of the vibrational structure of the C 1 state. The observation of electronically excited Xe fragments following excitation to the C state rotational levels of f parity indicates that the C state is predissociated by the electronic state of 0(-) symmetry associated with the Ar((1)S(0)) + Xe(6s(')[1/2](0) (o)) dissociation limit. The observed predissociation dynamics differ both qualitatively and quantitatively from the behavior reported in previous investigations. An adiabatic two-state coupling model has been derived which accounts for the irregularities observed in the rovibronic and hyperfine level structure of the C 1 state. The model predicts the existence of a second state of Ω = 1 symmetry, supporting several tunneling/predissociation resonances located ~200 cm(-1) above the C 1 state.

Site-specific solvent exposure analysis of a membrane protein using unnatural amino acids and 19F nuclear magnetic resonance

Membrane proteins play an essential role in cellular metabolism, transportation and signal transduction across cell membranes. The scarcity of membrane protein structures has thus far prevented a full understanding of their molecular mechanisms. Preliminary topology studies and residue solvent exposure analysis have the potential to provide valuable information on membrane proteins of unknown structure. Here, a 19F-containing unnatural amino acid (trimethylfluoro-phenylalanine, tfmF) was applied to accomplish site-specific 19F spin incorporation at different sites in diacylglycerol kinase (DAGK, an Escherichia coli membrane protein) for site-specific solvent exposure analysis. Due to isotope effect on 19F spins, a standard curve for 19F-tfmF chemical shifts was drawn for varying solvent H2O/D2O ratios. Further site-specific 19F solvent isotope shift analysis was conducted for DAGK to distinguish residues in water-soluble loops, interfacial areas or hydrophobic membrane regions. This site-specific solvent exposure analysis method could be applied for further topological analysis of other membrane proteins.

Comparative in Situ DRIFTS-MS Study of12CO- and13CO-TPR on CuO/CeO2Catalyst

A ceria-supported copper oxide catalyst has been examined with respect to interaction with CO by means of CO-TPR tests employing a DRIFTS cell as reactor. Parallel analysis of isotopic shifts in the DRIFTS spectra obtained upon interaction of the catalysts with either 12CO or 13CO allows unambiguous assignment of the various carbonyl and carbonate-type species formed. The study is complemented by separate examination of the stability of carbonyl species focused to get hints on the nature of CO adsorption centers at the catalyst surface. Joint analysis of gases evolution during the CO-TPR tests and DRIFTS spectra is employed to determine the nature of processes taking place during such tests. Additionally, analysis of the various CO2 isotopes evolving during the course of a TPO run subsequent to 13CO-TPR test is employed to discard the occurrence of CO disproportionation upon interaction of the catalyst with CO up to 400 °C.

Dynamics of Rhodobacter capsulatus [2Fe-2S] Ferredoxin VI and Aquifex aeolicus Ferredoxin 5 via Nuclear Resonance Vibrational Spectroscopy (NRVS) and Resonance Raman Spectroscopy

We have used (57)Fe nuclear resonance vibrational spectroscopy (NRVS) to study the Fe(2)S(2)(Cys)(4) sites in oxidized and reduced [2Fe-2S] ferredoxins from Rhodobacter capsulatus (Rc FdVI) and Aquifex aeolicus (Aa Fd5). In the oxidized forms, nearly identical NRVS patterns are observed, with strong bands from Fe-S stretching modes peaking around 335 cm(-1), and additional features observed as high as the B(2u) mode at approximately 421 cm(-1). Both forms of Rc FdVI have also been investigated by resonance Raman (RR) spectroscopy. There is good correspondence between NRVS and Raman frequencies, but because of different selection rules, intensities vary dramatically between the two kinds of spectra. For example, the B(3u) mode at approximately 288 cm(-1), attributed to an asymmetric combination of the two FeS(4) breathing modes, is often the strongest resonance Raman feature. In contrast, it is nearly invisible in the NRVS, as there is almost no Fe motion in such FeS(4) breathing. NRVS and RR analysis of isotope shifts with (36)S-substituted into bridging S(2-) ions in Rc FdVI allowed quantitation of S(2-) motion in different normal modes. We observed the symmetric Fe-Fe stretching mode at approximately 190 cm(-1) in both NRVS and RR spectra. At still lower energies, the NRVS presents a complex envelope of bending, torsion, and protein modes, with a maximum at 78 cm(-1). The (57)Fe partial vibrational densities of states (PVDOS) were interpreted by normal-mode analysis with optimization of Urey-Bradley force fields. Progressively more complex D(2h) Fe(2)S(2)S'(4), C(2h) Fe(2)S(2)(SCC)(4), and C(1) Fe(2)S(2)(Cys)(4) models were optimized by comparison with the experimental spectra. After modification of the CHARMM22 all-atom force field by the addition of refined Fe-S force constants, a simulation employing the complete protein structure was used to reproduce the PVDOS, with better results in the low frequency protein mode region. This process was then repeated for analysis of data on the reduced FdVI. Finally, the degree of collectivity was used to quantitate the delocalization of the dynamic properties of the redox-active Fe site. The NRVS technique demonstrates great promise for the observation and quantitative interpretation of the dynamical properties of Fe-S proteins.

Vibrations of the Phenoxyl Radical

Phenoxyl radical (C(6)H(5)O) was prepared photochemically in low-temperature argon matrices. The infrared absorption spectra were obtained for C(6)H(5)O and for the isotopically labeled species C(6)D(5)O and 1-(13)C(12)C(5)H(5)O. All but one IR-active fundamental vibrations were detected, most of them not previously observed. Combination of results from IR linear dichroism measurements on photooriented samples, determination of absolute IR intensities with the help of internal standards, analysis of isotopic shifts, and quantum chemical predictions (B3LYP/cc-pVTZ) led to a detailed assignment of phenoxyl radical vibrations. Significant frequency shifts are observed with respect to previously reported data based on resonance Raman studies in polar solutions. For some vibrations, these shifts reflect environment-induced structural changes, such as increase of the quinoid character of the phenoxyl radical in polar media. In particular, the frequency of the CO stretching vibration, readily observable in both IR and Raman experiments, is extremely sensitive to the environment and can thus be used to probe its polarity.

Isotope shifts in finite nuclei and the pairing properties of nuclear matter

A uniform nuclear matter with s-wave pairing is studied within the local energy-density functional approach, incorporating a few parameter sets extracted from the analysis of isotope shifts in finite nuclei. The dilute limit, in which the regime changes from weak to strong pairing, is considered in detail, and, for strong coupling, the ground state properties of that system are found to be completely determined in leading order by the singlet scattering length ann. The combination of a density-dependent contact pairing interaction and an energy cutoff adjusted to produce a realistic value of ann is shown to be the preferred choice among the deduced parameter sets.

Interstitial oxygen in germanium and silicon

The microscopic structure of interstitial oxygen in germanium and its associated dynamics are studied both experimentally and theoretically. The infrared absorption spectrum is calculated with a dynamical matrix model based on first-principles total-energy calculations describing the potential energy for the nuclear motions. Spectral features and isotope shifts are calculated and compared with available experimental results. From new spectroscopic data on natural and on quasimonoisotopic germanium samples, new isotope shifts have been obtained and compared with the theoretical predictions. The low-energy spectrum is analyzed in terms of a hindered rotor model. A fair understanding of the center is achieved, which is then compared with interstitial oxygen in silicon. The oxygen atom is nontrivially quantum delocalized both in silicon and in germanium, but the physics is shown to be very different: while the Si-O-Si quasimolecule is essentially linear, the Ge-O-Ge structure is puckered. The delocalization in a highly anharmonic potential well of oxygen in silicon is addressed using path-integral Monte Carlo simulations, for comparison with the oxygen rotation in germanium. The understanding achieved with this new information allows us to explain the striking differences between both systems, in both the infrared and the far-infrared spectral regions, and the prediction of the existencemore » of hidden vibrational modes, never directly observed experimentally, but soundly supported by the isotope-shift analysis. {copyright} {ital 1997} {ital The American Physical Society}« less

Measurement and analysis of isotope shifts in 151,153Eu+ from hyperfine spectra.

Isotope shifts in $^{151,153}\mathrm{Eu}^{+}$ have been measured for four optical transitions between the metastable levels 4${\mathit{f}}^{7}$${(}^{8}$S\ifmmode^\circ\else\textdegree\fi{})5${\mathit{d}}^{9}$D${\mathrm{\ifmmode^\circ\else\textdegree\fi{}}}_{\mathit{J}}$ and the excited levels 4${\mathit{f}}^{7}$${(}^{8}$S${\mathrm{\ifmmode^\circ\else\textdegree\fi{}}}_{7/2}$)6${\mathit{p}}_{3/2}$;J' in a collinear laser and slow-ion-beam apparatus. A phenomenological interpretation and an ab initio calculation have been made and compared with experiment.

Electron diffraction investigation of the structure of a molecule of zinc difluoride

The available data in the literature on the molecular constants of ZnF 2 are totally contradictory. The authors of an electron diffraction investigation [4] carried out using the visual method recommend a linear structure for this molecule. The absence of defocusing of the molecular beams in an inhomogeneous electric field led the authors of [5] to an analogous conclusion. At the same time, from an analysis of isotopic shifts of the frequency of the ant• oscillation v3 [6, 7] we have concluded that the ZnF 2 molecule is characterized by an angular equilibrium configuration. However it is essential to note that on the basis of these very same values of the isotope effects the authors of [6-9] give different values for the bond angle F--Zn--F: 157 • 2 ~ [6], 165 • 8 ~ [8], 160-180 ~ [9], 150 ~ [7]. Quantum chemical calculations [I0], which come out in favor of a linear structure for zinc difluoride, lead to numerical values for the internuclear distance r(Zn-F) and the frequency of the totallysymmetric vibration ~I , of 1.74 ~ and 719 cm -I respectively. These values do not agree with experimental data obtained in electron diffraction [4] and spectroscopic [7] investigations.

Parametric analysis of isotope shifts without the use of the normal mass shift

The recently reformulated theory of the mass shift contribution to atomic isotope shifts is applied in a parametric analysis of isotope shifts in Mo. Parameters representing relativistic effects in the isotope shifts are derived and discussed.

Reformulation of the theory of the mass shift

The conventional division of the mass shift in atomic spectra into normal and specific mass shift is shown to lead to cancellation between the two terms in heavy atoms. It is suggested that the evaluation of the NMS in terms of the binding energy of a level is potentially unreliable, and certainly complicates unnecessarily the relativistic corrections to the mass shift. A mass shift Hamiltonian is derived, including relativistic corrections to order 1/c2, and the physical significance of the terms discussed. The Hamiltonian is given in two equivalent forms, for use with non-relativistic and relativistic wavefunctions. The implications for parametric analysis of isotope shifts are discussed.

The N-dependence of Cd mean square charge radii (54 ⩽ N ⩽72) and the nuclear moments of 103Cd

The isotope shift of the radioactive Cd isotopes 102Cd, 103Cd, 104Cd, 105Cd, 107Cd, 111Cd, 113Cd, 115Cd, 117Cd, 118Cd, 119Cd, 120Cd and the hyperfine structure Splitting of 103Cd are determined in the CdI 5s 2 1S 0-5s5p 3P 1, λ = 326.1 nm line by fluorescence laser spectroscopy using a pulsed laser system and frequency doubling. The unstable Cd isotopes are produced at the ISOLDE mass separator at CERN and are investigated on-line in a resonance vessel. Changes of mean square charge radii are derived from the isotope shift data. The curve of the radii as a function of the mass number, shows on top of the regular A 1 3 expansion a collective contribution of parabolic shape which peaks at N = 66 in the middle of the shell. This contribution is considerably stronger than calculated from the B(E2 + 1) values solely. Isotonic and isobaric shifts between Z = 37 and Z = 56 are obtained in a combined analysis of isotope shifts ( δ〈 r 2〉), muonic 〈 r 2〉 values and B(E2 + 1) values. The shifts agree with the predictions of the droplet model showing the buildup of a neutron skin along isobaric chains. The nuclear moments of 103Cd have been determined as μ I , = −0.81(3) μ n and Q s = −0.79(66)b.

State dependent volume isotope shift analysis of the low lying states of Ba I and Ba II.

Relativistic multi-configuration Dirac-Fock wavefunctions, coupled to good angular momentum J, have been calculated for low lying states of Ba I and Ba II. The resulting electronic factors show good agreement with data derived from recent high-resolution laser spectroscopy experiments and results from a comparison of muonic and optical data.

The I, I′, and I″ absorption bands of O 2 in the region 790–865 Å

The absorption spectra of 16O 2 and 18O 2 in the wavelength region 790–865 Å have been photographed with a 6.65-m vacuum spectrograph. The bands are diffuse and most of them are classified as members of three vibrational progressions, I, I′, and I″, which originate from the v = 0 level of the ground state of oxygen. Absolute vibrational quantum number assignments are made for each of these progressions based on isotope shift analysis, and the vibrational constants of their upper electronic states are reported for 16O 2 and 18O 2. The similarity in vibrational constants between these electronic states and those for the a 4Π ui state of O 2 +, as well as their quantum defects suggest that they are Rydberg states. In addition, the magnitude of their spin-orbit splitting and the rotational structure for some of these bands indicate that the upper electronic state for each of these three progressions has 3Π u symmetry.

Spins, magnetic moments, and isotope shifts ofNa21−31by high resolution laser spectroscopy of the atomicD1line

A polyisotopic sodium beam produced by reactions of 20 GeV protons in an uranium target, was illuminated with a tunable cw dye laser. The atomic beam is analyzed by a six-pole magnet, ionized, and detected after selection of one isotope by use of a mass spectrometer. From the optical ${D}_{1}$ resonance lines the hyperfine structure, magnetic moments, and isotope shifts of $^{21\ensuremath{-}31}\mathrm{Na}$ have been determined. The nuclear spins of $^{26\ensuremath{-}30}\mathrm{Na}$ have been measured by magnetic resonance. The results are discussed in terms of nuclear deformation. The analysis of isotope shifts shows the presence of an appreciable volume shift contribution.NUCLEAR STRUCTURE $^{26\ensuremath{-}30}\mathrm{Na}$; measured $J$. $^{21\ensuremath{-}31}\mathrm{Na}$; measured isotope shifts; deduced $\ensuremath{\mu}$. Atomic beam laser spectroscopy and magnetic resonance.