Isotopic Splitting Research Articles

Tautomerism and isotopic multiplets in the 13C NMR spectra of partially deuterated 3‐arylpyrimido[4,5‐c]pyridazine‐5,7(6H,8H)‐diones and their sulfur analogs—evidence for elucidation of the structure backbone and tautomeric forms

The tautomerism of the synthesized 3-arylpyrimido[4,5-c]pyridazine-5,7(6H,8H)-diones (1a-d) and 3-aryl-7-thioxo-7,8-dihydro-6H-pyrimido[4,5-c]pyridazine-5-ones (2a-d) was studied in dimethyl sulfoxide (DMSO)-d(6). (1)H NMR spectra of 1a-d showed a clustered water molecule in the structure backbone that is attached by strong intermolecular H bonding. The relation between the temperature and H bonding of the clustered water molecule with 1a was also studied as representative. The relation between the electronegativity (chi) of the substituent on phenyl ring and the chemical shifts of clustered water protons in 1a-d was also studied. All of 1a-d and also 2d compounds existed in lactam (I) form, whereas 2a-c compounds have two distinguished tautomers in DMSO-d(6) [lactam (I) and lactim (II) forms]. The solvent-substrate proton exchange was examined in compounds 1a-d and 2a-d by adding one drop of D(2)O. All compounds (except 1d) showed proton/deuterium exchange of the clustered water protons in DMSO by adding one drop of D(2)O. Some compounds (but not all of them) that are easily soluble in DMSO-d(6) containing D(2)O showed isotopic splitting (beta-isotope effect) in their (13)C NMR spectra. Among them, compound 1a was the best evidence to help the spectral assignments and structure determination of predominant tautomer by carbon-13 splitting (beta-isotope effect).

Reactions of ruthenium and rhodium atoms with carbon monoxide and dinitrogen mixtures: A combined experimental and theoretical study

Laser-ablated Ru and Rh atoms react with CO and N(2) mixture in excess neon to produce the carbonylmetal dinitrogen complexes, (NN)(n)MCO (M=Ru,Rh; n=1,2) and NNRu(CO)(2), as well as metal carbonyls and dinitrogen complexes. These carbonylmetal dinitrogen complexes are characterized using infrared spectroscopy on the basis of the results of the isotopic substitution and mixed isotopic splitting patterns. Density functional theory calculations have been performed on these complexes. Overall agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts supports the identification of these species from the matrix infrared spectra. Furthermore, a plausible reaction pathway for the formation of the products has been proposed. This work reveals that the reactivity of Ru and Rh atoms toward CO is prior to N(2).

A Combined Experimental and Theoretical Study of Iron Dinitrogen Complexes: Fe(N2), Fe(NN)x (x = 1−5), and Fe(NN)3−

Reactions of laser-ablated iron atoms with dinitrogen in excess neon produce the iron dinitrogen complexes Fe(N(2)), Fe(NN)(x) (x = 1-5), and Fe(NN)(3)(-) through capture of the ablated electron. The reaction products are characterized on the basis of isotopic shifts, mixed isotopic splitting patterns, stepwise annealing, change of reagent concentration and laser energy, CCl(4)-doping experiments, and comparison with theoretical predictions from density functional theory calculations. The overall agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts supports the identification of these species from the matrix infrared spectra. Natural bond orbital analysis and reaction pathways for the formation of the products are discussed.

Single-frequency laser spectroscopy of the boron bound exciton inS28i

While the first comparison of shallow bound exciton photoluminescence between natural Si and highly enriched $^{28}\text{S}\text{i}$ dramatically demonstrated the importance of inhomogeneous isotope broadening, the transitions in $^{28}\text{S}\text{i}$ were in fact too narrow to be resolved with the then available instrumental resolution of $0.014\text{ }{\text{cm}}^{\ensuremath{-}1}$. We report results for the boron bound exciton transition in highly enriched $^{28}\text{S}\text{i}$ using a novel apparatus for photoluminescence excitation spectroscopy based on a tuneable single-frequency laser source with sub-MHz resolution. Twenty well-resolved doublets, exhibiting a $^{10}\text{B}--^{11}\text{B}$ isotope splitting, are observed in the new spectra for $^{28}\text{S}\text{i}$ with isotopic enrichment $>99.99%$. Linewidths as narrow as $0.0012\text{ }{\text{cm}}^{\ensuremath{-}1}$ (150 neV) full width at half maximum are observed for the most highly enriched sample.

Reactions of Group 14 Metal Atoms with Acetylene: A Matrix Isolation Infrared Spectroscopic and Theoretical Study

Laser-ablated group 14 metal atoms have been codeposited at 4 K with acetylene in excess argon. Products, Ge(C2H2), HGeCCH, Sn(C2H2), Sn2CCH2, HSnCCH, and HPbCCH, have been formed in the present experiments and characterized using infrared spectroscopy on the basis of the results of the isotopic shifts, mixed isotopic splitting patterns, stepwise annealing, the change of reagent concentration and laser energy, and the comparison with theoretical predictions. Density functional theory calculations have been performed on these molecules. The agreement between the experimental and the calculated vibrational frequencies, relative absorption intensities, and isotopic shifts supports the identification of these molecules from the matrix infrared spectra. Plausible reaction mechanisms have been proposed to account for the formation of these molecules.

Tautomeric behaviour and isotopic multiplets in the 13C NMR spectra of partially deuterated 5‐arylazo‐pyrimidine (1H,3H,5H)‐2,4,6‐triones and 5‐arylazo‐2‐thioxo‐pyrimidine (1H,3H,5H)‐4,6‐diones—evidence for elucidation of tautomeric forms

NMR spectra of the synthesized azo dyes, 5-arylazo-pyrimidine (1H,3H,5H)-2,4,6-triones (5a-g), 1,3-dimethyl-5-arylazo-pyrimidine (1H,3H,5H)-2,4,6-triones (6a-g), and 5-arylazo-2-thioxo-pyrimidine (1H,3H,5H)-4,6-diones (7a-g) were studied in (CD(3))(2)SO (three drops of CD(3)OD were added into solutions of the dyes in two different concentrations). All dyes showed intramolecular hydrogen bonding. Dyes 5a-7a showed bifurcated intramolecular hydrogen bonds. Tautomeric behaviours of some of N-methylated azo dyes (6a-g) were studied in two different concentrations. The solvent-substrate proton exchange of dyes 5a-d, 6a and 7a-e was examined in presence of three drops of CD(3)OD. The dyes which were soluble in (CD(3))(2)SO containing CD(3)OD showed isotopic splitting (beta-isotope effect) in the (13)C NMR spectra.

Infrared spectra and density functional theory calculations of the tantalum and niobium carbonyl dinitrogen complexes

Laser-ablated tantalum and niobium atoms react with CO and N(2) mixtures in excess neon to produce carbonyl metal dinitrogen complexes, NNMCO (M = Ta, Nb), (NN)(2)TaCO, and NNTa(CO)(2), as well as metal carbonyls and dinitrogen complexes. These carbonylmetal dinitrogen complexes are characterized using infrared spectroscopy on the basis of the results of the isotopic substitution and mixed isotopic splitting patterns. Density functional theory calculations have been performed on these novel species. The good agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts supports the identification of these species from the matrix infrared spectra. Natural bond orbital analysis and plausible reaction mechanisms for the formation of the products are discussed.

Modelling of mercury isotope separation in CP stellar atmospheres: Results and problems

Formation of anomalous isotope abundances in the atmospheres of chemically peculiar (CP) stars can be explained by light-induced drift (LID). This effect is additional to the radiative acceleration and appears due to systematic asymmetry of radiative flux in partly overlapping isotopic spectral line profiles. LID causes levitation of an isotope with a red-shifted spectral line and sinking of an isotope with a blue-shifted line, generating thus diffusive separation of isotopes. We have studied diffusion of mercury as a typical well-studied isotope-rich heavy metal. Our model computations show that in mercury-rich quiescent atmospheres of CP stars LID causes levitation of the heavier mercury isotopes and sinking of the lighter ones. Precise quantitative modelling of the process of isotope separation demands very high-resolution computations and the high-precision input data, including data on hyperfine and isotopic splitting of spectral lines, adequate line profiles and impact cross-sections. Presence of microturbulence and weak stellar winds can essentially reduce the effect of radiative-driven diffusion.

A reanalysis of the à A1″−X̃ A1′ transition of CFBr

The laser induced fluorescence spectrum of the A (1)A(")-X (1)A(') transition of CFBr is presented, with selected bands recorded at sub-Doppler resolution, allowing the rotational constants to be fully determined. Analysis of dispersed fluorescence spectra and the pattern of (79)Br/(81)Br isotope splittings indicate that the origin must be shifted from previous assignments in the literature to 23 271.0 cm(-1). This implies that only the lowest four vibrational levels in the A state have significant quantum yields for fluorescence, with all other levels strongly predissociated. Comparison with photofragment measurements implies that the A state is metastable, with a barrier to dissociation of approximately 1000 cm(-1).

Infrared Spectrum and Anharmonic Force Field of CH2DBr

The gas-phase infrared spectrum of monodeuteromethyl bromide, CH2DBr, has been examined at medium resolution in the range 400-10000 cm(-1), leading to the identification of 70 vibrational transitions. The assignment of the absorptions in terms of fundamentals, overtones, combinations, and hot bands, assisted by quantum chemical calculations, is consistent all over the region investigated. The (79/81)Br isotopic splitting for the lowest fundamental nu6 and the value for the v8 = 1 level have been now precisely determined. Anharmonic resonances are very marginal for all fundamentals and the Coriolis interaction effects are clearly evident in the nu4/nu8 band system, in the nu2 and nu7 fundamentals. Spectroscopic parameters, obtained from the analysis of partially resolved rotational structure, have been derived in the symmetric tops limit approximation. High-quality ab initio calculations have been performed, and harmonic and anharmonic force fields have been predicted from coupled cluster CCSD(T) calculations employing the cc-pVTZ basis set. A good agreement between computed and experimental data, also including the C-H stretching overtones at 6000 and 9000 cm(-1), has been obtained.

Reactions of Rhodium and Ruthenium Atoms with Nitrous Oxide: A Combined Matrix Infrared Spectroscopic and Theoretical Study

Reactions of laser-ablated Rh and Ru atoms with N(2)O molecules in excess argon have been investigated using matrix-isolation infrared spectroscopy. Rhodium and ruthenium nitrous oxide complexes, M(NNO)(x) (M = Rh, Ru; x = 1, 2), have been observed and identified on the basis of isotopic shifts, mixed isotopic splitting patterns, and CCl(4)-doping experiments. Density functional theory calculations have been performed on the products. The overall agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts supports the identification of these species from the matrix infrared spectra. Furthermore, a plausible reaction mechanism for the formation of the products has been proposed.

Infrared spectroscopic and theoretical studies on the formation of Au2NO− and AunNO (n=2–5) in solid argon

Laser-ablated gold atoms have been codeposited at 4 K with nitric oxide in excess argon and the low temperature reactions of Au with NO in solid argon have been studied using infrared spectroscopy. The reaction products Au(2)NO(-), Au(2)NO, Au(3)NO, Au(4)NO, and Au(5)NO are formed in the present experiments and characterized on the basis of isotopic shifts, mixed isotope splitting patterns, stepwise annealing, the change in reagent concentration and laser energy, and comparison with theoretical predictions. Density functional theory calculations have been performed on these systems to identify possible reaction products. The agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts supports the identification of these molecules based on the matrix infrared spectra. Plausible reaction pathways have been proposed for the formation of these molecules.

Infrared Spectra of Transition-Metal Dioxide Anions: MO2−(M = Rh, Ir, Pt, Au) in Solid Argon

Transition-metal dioxide anions RhO(2)(-), IrO(2)(-), PtO(2)(-), and AuO(2)(-) were produced from cocondensation of laser-ablated metal atoms and electrons with dioxygen in excess argon at 6 K. Photosensitive absorptions were assigned to the antisymmetric stretching vibration (nu(3)) of the metal dioxide anions from isotopic shifts and splittings as well as theoretical frequency calculations. On the basis of the observed nu(3) vibrational frequencies for M(16)O(2) and M(18)O(2), the anions are estimated to be linear or near linear. Density functional calculations at the DFT/B3LYP level predicted that the third-row transition-metal dioxide anions IrO(2)(-), PtO(2)(-), and AuO(2)(-) have singlet, doublet, and triplet ground states with linear structures, while the RhO(2)(-) anion was predicted to have a slightly bent geometry.

Infrared Spectra and Density Functional Theory Calculations of Group 8 Transition Metal Sulfide Molecules

Small sulfur molecules were reacted with laser-ablated Fe, Ru, and Os atoms in excess argon and condensed at 7 K. Reaction products were identified from matrix infrared spectra through sulfur-34 isotopic shifts, spectra of sulfur isotopic mixtures, and frequencies from density functional calculations. The strongest absorptions of the MS(2) disulfide molecules are observed at 540.2, 535.5, and 537.5 cm(-1), respectively, for the group 8 metals, and a 523.2 cm(-1) band is assigned to the FeS vibrational fundamental in solid argon. The FeS(2)(-) anion was detected in the spectrum at 542.1 cm(-1). The RuS(2) absorption exhibited resolved natural ruthenium isotopic splittings. Evidence is also presented for side-bound M(S(2)) isomers and MS(4) molecules with different structures including Fe(S(2))(2), (S(2))RuS(2), and tetrahedral OsS(4). Although OsO(4) is a well-known molecule, this, we believe, is the first experimental observation of OsS(4).

Matrix Infrared Spectroscopic and Theoretical Studies on the Reactions of Late Lanthanoid Atoms with Nitrous Oxide in Excess Argon

Reactions of laser-ablated late lanthanoid atoms (Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) with N(2)O molecules in excess argon have been investigated using matrix-isolation infrared spectroscopy. Lanthanoid monoxide-dinitrogen complexes, OLn(N(2)) and OLnNN, are observed for Gd, Tb, Ho, and Er, and the OLnNN(+) cations are observed for Gd to Lu except for Yb. The new products are characterized on the basis of isotopic shifts, mixed isotopic splitting patterns, and CCl(4)-doping experiments. Density functional theory calculations have been performed on the new species, which support identification of the OLn(N(2)), OLnNN, and OLnNN(+) complexes from the matrix infrared spectra. Together with our earlier work involving early lanthanoid atoms, several trends are identified for the reactions of lanthanoid atoms with N(2)O molecules.

Reaction of Chloromethyl Radical with Dioxygen: Formation of the Chloromethylperoxy Radical and Its Photodissociation in Solid Argon

The reaction of chloromethyl radical with molecular oxygen in solid argon has been studied using matrix isolation infrared absorption spectroscopy. The chloromethyl radical was produced via codeposition of chloromethane with high frequency discharged argon atoms. The chloromethyl radical reacted with dioxygen spontaneously on annealing to form the chloromethylperoxy radical, which was characterized on the basis of isotopic splitting (Cl and O) as well as quantum chemical calculations. The chloromethylperoxy radical dissociated to give the weakly bound ClCO-H2O complex under UV light irradiation. The calculations predicted that the ClCO-H2O complex was produced by hydrogen atom transfer from a CHCl(O)-OH intermediate.

The Barium Isotopic Abundance in the Metal-Poor Star HD140283

AbstractWe derive the mixture of odd to even barium isotopes in the atmosphere of the metal-poor subgiant HD140283 from the analysis of the Ba ii transition at 4554 Å in a high-resolution high signal-to-noise spectrum of the star. The detailed shape of this spectral line depends on the relative contributions of odd and even isotopes via isotopic and hyperfine splitting. We measure the fractional abundance of odd Ba isotopes by modelling the formation of the Ba ii 4554-Å line profile with the use of both a classical 1D hydrostatic and a 3D hydrodynamical model atmosphere of HD140283. We interpret the results in terms of contributions by the slow (s) and rapid (r) neutron-capture processes to the isotopic mix. While the result of the 1D analysis of the Ba ii feature indicates a 64 ± 36% contribution of the r-process to the isotopic mix, the 3D analysis points toward a mere 15 ± 34% contribution from this process, that is consistent with a solar-like mixture of barium isotopes.

Spectral structure of 510.6 and 578.2 nm lines in a CuBr vapor laser

Considering the hyperfine structure and the isotopic splitting of copper active atomic levels, the temporal behavior of the spectral structure of amplified spontaneous emission at 510.6 nm line was calculated. The spectral line shapes of 510.6 and 578.2 nm laser lines were measured and compared with the calculated results at different experimental configurations, i.e., without cavity mirrors, with the back mirror, and with cavity mirrors. The results of the 578.2 nm line revealed that the mode competition was involved in the formation of laser oscillation.

Matrix Isolation Infrared Spectroscopic and Density Functional Theory Studies on the Reactions of Dysprosium Hydride with Carbon Monoxide

Abstract Laser-ablated dysprosium hydride has been co-deposited at 4 K with carbon monoxide in excess argon. Product HDyCO has been formed in the present experiments and characterized using infrared spectroscopy on the basis of the results of the isotopic shifts, mixed isotopic splitting patterns, stepwise annealing, and the comparison with theoretical predictions. Density functional theory calculations have been performed. The agreement between the experimental and calculated vibrational frequencies, and isotopic shifts supports the identification of the molecule from the matrix infrared spectra. A plausible reaction mechanism has been proposed to account for the formation of this molecule.

Reactions of Gold Atoms with Nitrous Oxide in Excess Argon: A Matrix Infrared Spectroscopic and Theoretical Study

Reactions of laser-ablated Au atoms with N(2)O molecules in excess argon have been investigated using matrix-isolation infrared spectroscopy and density functional theory calculation. On the basis of isotopic shifts, mixed isotopic splitting patterns, CCl(4)-doping experiments, and the comparison with theoretical calculations, the absorption at 2047.5 cm(-1) is assigned to the OAuNN(-) anion, and the absorption at 1512.3 cm(-1) is assigned to the AuNO(-) anion, respectively. No evidence is found for the formation of new neutral and cationic products in the present experiments. It is predicted that the OAuNN(-) anion is a linear singlet molecule and the AuNO(-) anion is a bent doublet molecule. The agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts supports the identifications of these species from the matrix infrared spectra. Plausible reaction pathways have also been discussed for the formation of these products.