Chlorine Nuclei Research Articles

Rotational spectrum, structure, and quadrupole coupling of cyclopropylchloromethyldifluorosilane.

Cyclopropylchloromethyldifluorosilane, c-C3H5SiF2CH2Cl, has been synthesized, and its rotational spectrum has been recorded by chirped-pulse Fourier transform microwave spectroscopy. The spectral analysis of several isotopologues indicates the presence of two distinct conformations in the free-jet expansion, which are interconvertible through a rotation of the chloromethyl group. A partial substitution structure is presented for the lower energy conformation and is compared to the equilibrium structure obtained from quantum chemical calculations. Additionally, the presence of the chlorine nucleus leads to the rotational transitions splitting into multiple hyperfine components and χaa, a measure of the electric field gradient along the a axis, is unusually small at merely +0.1393(73) MHz. Various common abinitio and density functional theory methods fail to predict good quadrupole coupling constants (in the principal axis system) that adequately reproduce the observed hyperfine splitting, although diagonalizing the quadrupole coupling tensor from the principal axis system into a nucleus-centered axis system reveals that, overall, these methods calculate reasonably the electric field gradient about the chlorine nucleus. Finally, a total of nine electric dipole forbidden, quadrupole allowed transitions are observed in the rotational spectra of the parent species of the higher energy conformation and the 37Cl isotopologue of the lower energy conformation. These include those of x-type (no change in parity of Ka or Kc), which, to our knowledge, is the first time such transitions have been observed in a chlorine-containing molecule.

Decay Characteristics of Neutron Excess Chlorine Nuclei

In neutron star mergers, neutron excess nuclei and the r-process are important factors governing the production of heavier nuclear systems. A single-particle model evaluation of chlorine nuclei suggests that the heaviest Z = 17 nucleus will have mass 62 with filling of the 1g9/2 neutron shell. A = 48 – 62 chlorine isotopes have limited experimental half-life data, but the model predicts beta decay half-lives in the range of 0.535 – 51.9 ms. Based on previous calculations for Z = 9 - 16, 20, 26, and 30 systems and comparisons to the 48Cl - 53Cl, and 55Cl calculations, summarized in the Japanese Nuclear Data Compilation, the single-particle model results likely overestimate the half-lives of A = 48 – 62 neutron excess chlorine nuclei.

The CLYC-7 scintillator as a fast neutron spectrometer: Pulse-shape discrimination for different neutron-induced reaction channels

The CLYC-7 scintillators (Cs2LiYCl6) are being studied for their capability to detect and discriminate both γ-ray radiation and neutrons in a wide energy range. Different Pulse-Shape Analysis (PSA) techniques were developed to perform this distinction, with excellent results. An intrinsic problem resides in the neutron detection mechanism, which occurs mainly via two nuclear reactions on the chlorine nucleus: 35Cl(n,p)35S and 35Cl(n,α)32P. In the latter, the neutron energy reconstruction turns out to be more difficult, due to the large variety of excited states (and therefore reaction Q values) of 32P. A particular PSA algorithm was investigated to perform this α background rejection, with interesting results in different energy ranges.

Measuring Yields and Angular Distributions of γ-Quanta from the Interaction between 14.1 MeV Neutrons and Sodium and Chlorine Nuclei

Measuring Yields and Angular Distributions of γ-Quanta from the Interaction between 14.1 MeV Neutrons and Sodium and Chlorine Nuclei

Neighborhood matters: Steric effects on methyl internal rotation and chlorine nuclear quadrupole coupling in 2-fluoro-4-chlorotoluene

The rotational spectrum of 2-fluoro-4-chlorotoluene was studied in the frequency range 4 to 24 GHz by Fourier transform microwave spectroscopy. Fine torsional splittings into doublets were found for all rotational transitions due to methyl internal rotation hindered with a barrier of about 230 cm−1. In combination with the quadrupole coupling hyperfine splittings on the same order of magnitude originating from the chlorine nucleus, rich spectral features were observed. Rotational and quadrupole coupling constants for the 35Cl and 37Cl isotopologues studied in natural abundance were precisely determined. Results from the experiment were supported by quantum chemical calculations at several levels of theory for the rotational constants and by Bailey's semi-experimental method for the quadrupole coupling constants. The χcc quadrupole coupling tensor element and the barrier to methyl internal rotation were compared with those of other halogen-substituted toluene derivatives.

Analysis of the Complex Quadrupole Hyperfine Patterns for Two Chlorine Nuclei in the Rotational Spectrum of 2,5-Dichlorothiophene.

The rotational spectrum of 2,5-dichlorothiophene (DCT) was measured for the first time using Fourier transform microwave spectroscopy from 5.5-19 GHz. Dense hyperfine splitting patterns due to the two quadrupolar chlorine nuclei (I = 3/2) were resolved and assigned for the 35Cl-35Cl, 37Cl-35Cl, and 37Cl-37Cl isotopologues and for the two 13C and one 34S analogues with two 35Cl atoms, allowing derivation of their respective nuclear quadrupole coupling tensors. The rotational constants obtained from fitting the spectra of the six isotopic species allowed derivation of the experimental geometry of DCT for comparison with the equilibrium structure computed at the MP2/aug-cc-pVTZ level. This revealed that the electron-withdrawing effect of chlorine causes small distortions in the ring geometry relative to thiophene, including a 1.1° increase in the two S-C-C angles and a 0.012 Å increase in the two S-C bond lengths.

Pure Rotational Spectrum of CCl+

Abstract The pure rotational spectrum of the CCl+ (X 1Σ+) cation has been observed for the first time using a cryogenic ion trap apparatus and applying an action spectroscopy scheme. The major isotopic species 12C35Cl+ was observed up to the J = 4 ← 3 transition around 191 GHz and 12C37Cl+ was observed up to J = 3 ← 2. All transitions exhibit (partially) resolved hyperfine structure from the presence of the chlorine nuclei (both I = 3/2). This study provides the data needed for future sensitive radio astronomical searches for CCl+ in space.

Rotational spectroscopy update for the newly identified atmospheric ozone depleter CF3CCl3

The pure rotational spectrum of CF3CCl3 (1,1,1-trichloro-2,2,2-trifluoroethane, CFC-113a) was investigated at 4–18 GHz in supersonic expansion with chirped pulse and cavity Fourier-transform rotational spectroscopy, and at 94–309 GHz with broadband millimetre wave spectroscopy. Spectroscopic constants for all four possible chlorine isotopic species have been considerably updated. Global fits of hyperfine-resolved and hyperfine-unresolved data are reported and triple chlorine nucleus hyperfine structure has been analysed for all four isotopologues to within experimental accuracy. The new measurements have been augmented with anharmonic force field calculations in an evaluation of the semi-experimental equilibrium geometry for CF3CCl3. Interactions between hyperfine sublevels contributing to frequencies of the lowest J transitions allowed determination of the axial rotational constant A = 1326.24(15) MHz for CF3C35Cl3 from analysis of pure rotational transitions.

Reoriention of diprotonated DABCO (1,4-Diazabicyclo[2.2.2]octane) cation and proton transfer in organic ferroelectric adduct DABCO-2(2-Chlorobenzoic acid)

Temperature dependences of 1H NMR as well as 35Cl NQR spin-lattice relaxation times T1 were investigated of a ferroelectric molecular adduct with Tc = 323 K, in which 1,4-diazabicyclo[2.2.2]octane (DABCO) is sandwiched between two 2-chlorobenzoic acid (2-ClBA). The NQR frequencies clearly show that proton transfer from 2-ClBA to DABCO is occurred and the molecular adduct consists of diprotonated DABCO cation and two 2-chlorobenzoate anions. The correlation time of reorientational motion of the diprotonated DABCO molecule was determined as a function of temperature. The activation energy Ea of the motion was estimated as 22 kJ mol−1 below Tc. The steep decrease of the NQR T1 with Ea = 50 kJ mol−1, observed above ca. 280 K in the ferroelectric phase, suggests a slow fluctuation of electric field gradient at chlorine nucleus.

Fourier transform microwave spectroscopy of the SiCl+ ion

Fourier transform microwave spectra for the J = 1 ← 0 and 2 ← 1 rotational transitions of the SiCl+ ion were observed for two isotopologues (35Cl and 37Cl) in the ground and the first excited vibrational states of the ground 1Σ+ electronic state. Thanks to the high resolution of the FTMW spectrometer, hyperfine structures due to the quadrupole moment of the chlorine nucleus and the nuclear spin-rotation interaction were fully resolved. The observed FTMW spectra were combined with previously reported MMW and diode laser spectra in an analysis to determine the mass-independent Dunham coefficients Uk,l as well as a mass scaling parameter Δ01Cl=-0.856(30). The equilibrium bond length of SiCl+ determined is re=1.9439729(10) Å and the nuclear quadrupole coupling constant of Si35Cl+ is eQqe=-11.8788(23) MHz.

Nuclear Magnetic Spectrometer for Studying Flows of Liquid Media

Elements of studies of flows of liquid media by a nuclear magnetic spectrometer are considered. Through an assessment of these features in the design of a nuclear magnetic spectrometer the relative concentrations of paramagnetic ions could be determined and the longitudinal and transverse relaxation times measured in flows of liquid media with error not more than 0.5%. A regime for recording the nuclear magnetic resonance signal of a flowing liquid of fluorine, phosphorous, lithium, boron, sodium, chlorine, and mercury nuclei is created. The results of experimental studies of flows of liquid media are presented.

Effects of Chlorination on the Tautomeric Equilibrium of 2-Hydroxypyridine: Experiment and Theory.

The effects of halogenation on the tautomeric and conformational equilibria of the model system 2-hydroxypyridine/2-pyridone have been investigated through chlorine substitution at positions 3, 4, 5, and 6. In the gas phase, the lactim syn-periplanar tautomer (OHs ) was the predominant species for all compounds over the lactam form (C=O) and the less abundant anti-periplanar lactim (OHa ). However, the population of the three species was shown to be dependent on the position of the chlorine substitution. Chlorination in position 5 or 6 strongly stabilizes the OHs tautomer, whereas the C=O form has a significant population when the ring is chlorinated in positions 3 or 4. Overall, the OHa form is the least favourable form, although the 3-substitution favours the population of this tautomer. In addition, the C=O tautomer is strongly stabilized in the solvent, which makes it the dominant form in some substituted species. This study has been performed by means of rotational spectroscopy in the gas phase and/or theoretical calculations in the isolated phase and in solution. Both the OHs and C=O forms of 5-chloro-2-hydroxypyridine and the OHs form of 6-chloro-2-hydroxypyridine were experimentally observed. All transitions displayed a complex nuclear hyperfine structure owing to the presence of the chlorine and nitrogen nuclei. For all species, a full quadrupolar hyperfine analysis has been performed. This has provided crucial information for the unambiguous identification of tautomers.

ЯКР 35CL И ЗАТОРМОЖЕННАЯ ПОДВИЖНОСТЬ В МОЛЕКУЛЯРНОМ КОМПЛЕКСЕ CL2·БЕНЗОЛ

Temperature dependences of the resonance frequency and the spin-lattice relaxation time of the chlorine nuclei are investigated in the equimolecular addition compound of chlorine with benzene in the temperature range between 77 K and the melting point. The experimental data reveal a complex picture of thermally activated molecular motion involving both components of this compound. At temperatures 77–130 K the quadrupole relaxation is determined by the action of three types of molecular motions: 1– background molecular librations, 2– reorientational movement of the benzene rings, modulating the electric field gradient at the chlorine nuclei, created by donor-acceptor interaction of the partner molecules, and 3– reorientational movement of the chlorine molecules at a rate less than the NQR frequency, causing the broadening of the 35 Cl spectral line and its fading out at 130 K. In this temperature region consistent separation of the respective contributions to the chlorine relaxation rate is made and the quantitative parameters of the movements defined. At higher temperatures, the development of hindered rotation of the chlorine molecules leads to the appearance of the resonance signal again at 150 K to ~4 MHz lower in frequency, and the relaxation time of the chlorine nuclei increases with increasing temperature. Both these facts indicate that the reorientation rate of the chlorine molecules becomes much higher than the nuclear quadrupole resonance frequency. By analogy with the known NQR data for 1,2-dichloroethane these results show that the “fast” reorientation of the chlorine molecule occurs about the axis that forms the angle ~14° with the Cl–Cl direction. The spin-lattice relaxation time of the chlorine nuclei, as measured in the field of both “slow” and “fast” reorientations, revealed that the activation energy of motion in these areas varies considerably (~22.5 kJ/mol and ~6.2 kJ/mol, respectively). The set of obtained data allows to conclude that at the temperatures 130–150 K in the sample, apparently, there are structural changes, leading to a sharp change in the mobility of the chlorine molecules. Received 0 7 .0 6 .201 6 ; accepted 23 .0 6 .201 6

Comprehensive analysis of the rotational spectrum of 2,2-dichloropropane

2,2-Dichloropropane, (CH3)2CCl2, is a globular, plastic crystal molecule characterised by an apparently featureless b-type rotational spectrum. The spectrum is complicated by relatively intense isotopic species, nuclear quadrupole hyperfine splitting from two chlorine nuclei, and clustering of the seven lowest normal modes of (CH3)2C35Cl2 in the wavenumber range 250–390cm-1. A comprehensive investigation of this spectrum was carried out on the basis of the room-temperature spectrum recorded up to 338GHz and of the supersonic expansion spectrum at cm-wave frequencies. The ground states of the (CH3)2C37Cl2 and 13CH312CH3C35Cl2 species were assigned for the first time and allowed redetermination of the molecular geometry. The double nucleus hyperfine structure was measured and analysed for both 35Cl2 and 35Cl37Cl species of 2,2-dichloropropane, and differences between orientations of the CCl bond axis and the hyperfine z-axis were determined and discussed. Rotational transitions in first excited states of all seven normal modes were found to be strongly perturbed requiring Coriolis type coupled fits for the (ν9,ν14) and (ν13,ν27) dyads, and the (ν26,ν8,ν21) triad. The precise vibrational energy differences lead to new values for the lowest normal mode frequencies.

Direct Investigation of Covalently Bound Chlorine in Organic Compounds by Solid‐State 35Cl NMR Spectroscopy and Exact Spectral Line‐Shape Simulations

35/37Cl NMR spectroscopy studies of organic systems are very rare, with only a few neat liquids having been studied.1 The lack of chlorine NMR spectroscopy data may be explained by the fact that 35Cl and 37Cl are quadrupolar (spin I=3/2) and low-frequency isotopes. The quadrupole moments of the chlorine nuclei couple with the electric field gradient (EFG) tensor at the nuclei; this phenomenon is known as the quadrupolar interaction (QI). The quadrupolar coupling constant, CQ, and the quadrupolar asymmetry parameter, ηQ, describe the magnitude and asymmetry of the QI. In solution, one of the consequences of the QI is fast relaxation, which means that the 35/37Cl NMR signals for covalently bound chlorines are very broad and are of low intensity.1 For these reasons, chemically distinct chlorine sites are very difficult to distinguish with solution NMR spectroscopy. However, in the solid state, nuclear spin relaxation is typically slower, thus enabling higher quality 35Cl NMR spectra to be collected, at least in principle. Unfortunately, the magnitude of the QI for covalently bound chlorines is very large because of the substantial, anisotropic EFG at the Cl atom, owing mainly to its electronic configuration when it forms a chlorine–carbon bond. Conventional wisdom is that such chlorine sites cannot be studied in powders by solid-state NMR spectroscopy as the central transition (CT; mI=1/2↔−1/2) can span tens of megahertz in typical commercially available magnetic fields. For this reason, only ionic chlorides2 and inorganic chlorides3 have been studied, as the EFG at these chlorides is often an order of magnitude smaller than at covalently bound chlorine atoms in organic molecules. The bonding environments for these types of chlorine atoms are substantially different from the environments in those chloride-containing molecules that have been studied previously.2, 3 A partial 35Cl NMR spectrum for hexachlorophene has been briefly mentioned in the literature.4 On the other hand, most of the interesting chlorine chemistry occurs when Cl is covalently bound to a carbon atom, where the chlorine atom often acts as a leaving group. Chlorine atoms are also important in many organic pharmaceuticals as well as in crystal design applications where they can form halogen bonds.5 Recent studies show that covalently bound chlorine is also important in biological chemistry where, for example, the tryptophan 7-halogenase was found to selectively chlorinate tryptophan moieties.6

HERSCHELOBSERVATIONS OF INTERSTELLAR CHLORONIUM

Using the Herschel Space Observatory's Heterodyne Instrument for the Far-Infrared, we have observed para-chloronium (H2Cl+) toward six sources in the Galaxy. We detected interstellar chloronium absorption in foreground molecular clouds along the sight lines to the bright submillimeter continuum sources Sgr A (+50 km s−1 cloud) and W31C. Both the para-H352Cl+ and para-H372Cl+ isotopologues were detected, through observations of their 111–000 transitions at rest frequencies of 485.42 and 484.23 GHz, respectively. For an assumed ortho-to-para ratio (OPR) of 3, the observed optical depths imply that chloronium accounts for ∼4%–12% of chlorine nuclei in the gas phase. We detected interstellar chloronium emission from two sources in the Orion Molecular Cloud 1: the Orion Bar photodissociation region and the Orion South condensation. For an assumed OPR of 3 for chloronium, the observed emission line fluxes imply total beam-averaged column densities of ∼2 × 1013 cm−2 and ∼1.2 × 1013 cm−2, respectively, for chloronium in these two sources. We obtained upper limits on the para-H352Cl+ line strengths toward H2 Peak 1 in the Orion Molecular cloud and toward the massive young star AFGL 2591. The chloronium abundances inferred in this study are typically at least a factor ∼10 larger than the predictions of steady-state theoretical models for the chemistry of interstellar molecules containing chlorine. Several explanations for this discrepancy were investigated, but none has proven satisfactory, and thus the large observed abundances of chloronium remain puzzling.

Structure and properties of the (HCl)2H2O cluster observed by chirped-pulse Fourier transform microwave spectroscopy

The rotational spectrum of the cyclic (HCl)(2)H(2)O cluster has been identified for the first time in the chirped pulse, Fourier transform microwave spectrum of a supersonically expanded HCl/H(2)O/Ar mixture. The spectrum was measured at frequencies 6-18.5 GHz, and transitions in two inversion-tunneling states, at close to 1 : 3 relative intensity, have been assigned for the parent species. The two single (37)Cl isotopic species, and the double (37)Cl species have been assigned in the natural abundance sample, and the (18)O and HDO species of the cluster were identified in isotopically enriched samples. The rich nuclear quadrupole hyperfine structure due to the presence of two chlorine nuclei has been satisfactorily fitted and provided useful information on the nonlinearity of intermolecular bonds in the cluster. The r(s) heavy atom geometry of the cluster was determined and the strongest bond in the intermolecular cycle r(O···HCl) = 3.126(3) Å, is found to be intermediate in length between the values in H(2)O···HCl and (H(2)O)(2)HCl. The fitted spectroscopic constants and derived molecular properties are compared with ab initio predictions, and a discussion of complexation effects in these three clusters is made.

Dynamic Nuclear Polarization with Polychlorotriphenylmethyl Radicals: Supramolecular Polarization-Transfer Effects

Ups and downs of DNP: Polychlorinated trityl radicals (see structure: C black, Cl green, Na gray, O red) used for dynamic nuclear polarization (DNP) showed a new transfer mechanism involving quadrupolar chlorine nuclei. The observation of positive or negative enhancements, depending on the substrate, highlights the supramolecular character of the initial polarization-transfer process.

Polychlorinated trityl radicals for dynamic nuclear polarization: the role of chlorine nuclei

Polychlorinated trityl radicals bearing carboxylate substituents are water soluble persistent radicals that can be used for dynamic nuclear polarization. In contrast to other trityl radicals, the polarization mechanism differs from the classical solid effect. DFT calculations performed to rationalize this behaviour support the hypothesis that polarization is transferred from the unpaired electron to chlorine nuclei and from these to carbon by spin diffusion. The marked differences observed between neutral and anionic forms of the radical will be discussed.

The Nature of Halogen⋅⋅⋅Halogen Interactions: A Model Derived from Experimental Charge‐Density Analysis

Slightly attractive: The attractive and anisotropic nature of the ClCl interaction in C(6)Cl(6) is experimentally demonstrated from an expansion of the electron density rho(r) around the chlorine nuclei. The interaction is explained in a model in which there is a bonding attraction involving electron-deficient (see picture, blue) and electron-rich (red) regions of adjacent Cl atoms.