Nuclear Spin-rotation Coupling Constants Research Articles

Simulation and analysis of 13C spin-rotation nuclear magnetic resonance relaxation rates of methyl groups

This work analyzes the nuclear spin–rotation contribution to the nuclear magnetic resonance relaxation of methyl groups from 10 rigid compounds (eight benzene derivatives with one, two, or three methyl groups and two bicyclic molecules) with internal rotation axes not aligned to the smallest molecular moment of inertia via molecular dynamics simulation and ab initio calculation. The molecular dynamics simulation and ab initio calculation of nuclear spin-rotation coupling constants reproduce the experimental behavior in selected systems. The presented methodology can help in the analysis and interpretation of experimental relaxation data.

Microwave spectrum and iodine nuclear quadrupole coupling constants of 1,1-diiodoethane

The high resolution rotational spectroscopic observation of 1,1-diiodoethane is investigated using a pulsed jet, cavity Fourier transform microwave (FTMW) spectrometer over the frequency range 11.5–18 GHz for the first time. The rotational constants, the centrifugal distortion constants, the nuclear spin-rotation coupling constants, and the complete tensor components of the nuclear quadrupole coupling for both iodine nuclei have been determined and reported. The fitted rotational constants are A = 4548.320446(47), B = 625.629141(55), C = 558.798939(43) MHz and the nuclear quadrupole coupling constants are χaa = −1089.8125(7), χbb − χcc = −542.3162(13), |χab| = 1215.7505(10), χbc = 340.8983(14), and |χac| = 562.4206(19) MHz. No A-E splittings due to the methyl group internal rotation were observed. Many dipole-forbidden/electric quadrupole coupling allowed transitions were observed in the spectrum due to the large iodine quadrupole coupling effect. Quantum chemical calculations were performed at the CCSD(T)/aug-cc-pVTZ-pp level of theory. The calculated rotational constants, centrifugal distortion constants, and hyperfine constants were used to guide the data analysis.

Terahertz spectroscopy of methanimine and its isotopologs

Context. Methanimine (CH2NH) is a simple molecule composed of methylene and imine. The molecule has been detected toward the Galactic center, star-forming regions, circumstellar envelopes, and other galaxies since 1973. In previous studies, the rest frequency of methanimine has been measured for normal species up to the 650-GHz region, but its 13 CH2NH, CH2 15 NH, and CH2ND isotopologs were limited to the 100-GHz region. Aims. If a rotational temperature of 100 K is assumed for methanimine, the highest intensity falls at approximately 1.5 THz. In addition to normal methanimine, the 13 CH2NH, CH2 15 NH, and CH2ND isotopologs in their ground-vibrational states were observed in the frequency range of 120–1600 GHz to provide accurate rest frequency information. Based on this study, the calculated rest frequencies below 2 THz should be sufficiently precise and support observations using all ALMA and Herschel/HIFI observational bands. Methods. Methanimine was generated by pyrolysis of diaminoethane (DAE) vapor at 850 ◦ C. 13 CH2NH and CH2 15 NH isotopologs were measured with their natural abundance, and deuterization of DAE was performed by mixing normal DAE with deuterated water, D2O, and then pyrolyzed. This gives the deuterated isotopolog of methanimine, CH2ND. Spectral measurements were performed by using the 23 kHz source-frequency modulated terahertz spectrometer at Toho University. Results. Both a -a ndb-type transitions up to 1.6 THz for the three isotopologs and the normal species were measured. Rotational and centrifugal distortion constants for the three isotopologs were accurately determined. For normal species (CH2NH), both electric quadrupole and nuclear spin-rotation coupling constants for nitrogen nucleus were determined, while for the 13 CH2NH and CH2ND species, only electric quadrupole-coupling constants for nitrogen nucleus were determined. Conclusions. Our spectral line frequencies are suitable for a future astronomical search for these isotopologs of methanimine. The 1σ frequency accuracy up to 2 THz is lower than 100 kHz.

Fourier-transform microwave spectroscopy of the H2–H2O complex

Fourier-transform microwave spectroscopy was applied to observe the J=1–0 rotational transition of the ortho-H2–H2O complex and isotopologues in the ground Σ0 state (H2 in the jH2=1 state and H2O in the ground 000 state) to obtain precise molecular constants. Observed spectra were split into three hyperfine components, confirming the complexes are the ortho-H2/para-D2 species. The determined nuclear spin–spin coupling constant indicates H2 is rotating almost freely in the complex; the Σ0 state is nearly of jH2=1 and kH2=0. For the ortho-H2 species, the nuclear spin–rotation coupling constant was also determined.

New Experimental NMR Shielding Scales Mapped Relativistically from NSR: Theory and Application.

The recently proposed relativistic mapping between nuclear magnetic resonance (NMR) shielding and nuclear spin-rotation (NSR) coupling tensors [J. Chem. Phys. 2013, 138, 134104] is employed to establish new experimental (more precisely, experimentally derived) absolute shielding constants for H and X in HX (X = F, Cl, Br, and I). The results are much more accurate than the old "experimental" values that were based on the well-known nonrelativistic mapping. The relativistic mapping is very robust in the sense that it is rather insensitive to the quality of one-particle basis sets and the treatment of electron correlation. Relativistic effects in the NSR coupling constants are also elucidated in depth.

The Zeeman effect and hyperfine interactions in J = 1–0 transitions of CH+ and its isotopologues

The J = 1-0 transitions of (12)CH(+), (13)CH(+), and (12)CD(+) in the ground X(1)Σ(+) state have been unambiguously identified by using an extended negative glow discharge as an ion source. Unexpectedly large Zeeman splittings have been observed, and the (13)CH(+) line exhibits nuclear spin-rotation hyperfine splitting in addition to the Zeeman effect. The nuclear spin-rotation coupling constant was determined to be 1.087(50) MHz for the (13)C species. The rotational g-factor is found to be -7.65(29), in terms of the nuclear magneton for the J = 1 and v = 0 state, more than an order of magnitude larger than values for typical diamagnetic closed shell molecules. These larger than usual magnetic interactions for a (1)Σ molecule are caused by the large rotational energy and relatively small excitation energy of the excited A(1)Π state. The effective g-factor and the spin-rotation coupling constant obtained by ab initio calculations agree very well with the experimentally determined values.

Determination of nuclear spin–rotation coupling constants in CF 3I by chirped-pulse Fourier-transform microwave spectroscopy

The rotational spectrum of CF 3I in the ground vibrational state has been re-measured using a chirped-pulse Fourier-transform microwave spectrometer recently constructed at the University of Bristol. The new spectrometer provides the capability to acquire broadband rotational spectra throughout an operational frequency range of 7–18 GHz. The frequencies of ninety-nine F 1′– F 1″ transitions in three distinct J K ′– J K ″ bands have been recorded during an experiment which required only a couple of hours of data collection. Many of these transitions have additionally been re-measured using a Balle–Flygare, Fourier-transform microwave spectrometer. Fitting the data to the Hamiltonian for a C 3v prolate, symmetric top has allowed the determination of new spectroscopic parameters. The rotational constant, B 0, and nuclear quadrupole coupling constant, χ aa ( I ) , are consistent with the results provided in earlier works. The nuclear magnetic spin–rotation constants, C perp.(I) and C perp.(F), have been independently determined for the first time. These parameters are evaluated as 6.92(5) kHz and 2.37(11) kHz respectively. A technical description of the new CP-FTMW instrument is presented.

Rotational spectra, potential function, Born–Oppenheimer breakdown and magnetic shielding of SiSe and SiTe

The pure rotational spectra of 18 isotopic species of SiSe (8) and SiTe (10) have been measured in their X 1Σ + electronic state with a pulsed-jet resonator Fourier transform microwave spectrometer. The molecules were prepared by a combined DC discharge/laser ablation technique and stabilised in a supersonic jet of Ar. Global multi-isotopologue analyses yielded spectroscopic Dunham parameters Y 01, Y 11, Y 21, Y 31 and Y 02 for both species, as well as effective Born–Oppenheimer breakdown (BOB) coefficients δ 01 for Si, Se and Te. A direct fit of the same data sets to an appropriate radial Hamiltonian yielded analytic potential energy functions and BOB radial functions for the X 1Σ + electronic state of both SiSe and SiTe. Additionally, the magnetic hyperfine interactions produced by the uneven mass number A nuclei 29Si, 77Se and 125Te were observed, yielding first determinations of the corresponding nuclear spin–rotation coupling constants.

Pure rotational spectra of PbSe and PbTe: potential function, Born–Oppenheimer breakdown, field shift effect and magnetic shielding

The pure rotational spectra of 41 isotopic species of PbSe and PbTe have been measured in their X 1Sigma+ electronic state with a resonator pulsed-jet Fourier transform microwave spectrometer. The molecules were prepared by laser ablation of suitable target rods and stabilised in supersonic jets of noble gas. Global multi-isotopologue analyses yielded spectroscopic Dunham parameters Y01, Y11, Y21, Y31, Y02, and Y12 for both species, as well as effective Born-Oppenheimer breakdown (BOB) coefficients delta01 for Pb, Se and Te. Unusual large values of the BOB parameters for Pb have been rationalized in terms of finite nuclear size (field shift) effect. A direct fit of the same data sets to an appropriate radial Hamiltonian yielded analytic potential energy functions and BOB radial functions for the X 1Sigma+ electronic state of both PbSe and PbTe. Additionally, the magnetic hyperfine interactions produced by the uneven mass number A nuclei 207Pb, 77Se, 123Te, and 125Te were observed, yielding first determinations of the corresponding nuclear spin-rotation coupling constants.

Lamb-dip millimeter-wave spectroscopy of HCP: Experimental and theoretical determination of 31P nuclear spin–rotation coupling constant and magnetic shielding

The semi-stable HCP molecule has been produced by gas phase copyrolysis of phosphine and chloroform. The three rotational transitions J = 2 ← 1, 3 ← 2, and 4 ← 3 have been recorded with sub-Doppler resolution using the Lamb-dip technique. The hyperfine structure due to the magnetic coupling between rotation and phosphorus nuclear spin has been resolved, yielding the value of the phosphorus spin–rotation constant, C(P) = 43.64 ± 0.15 kHz, from which the corresponding absolute magnetic shielding has been derived: σ(P) = 373 ± 2 ppm. Theoretical values of C(P) and σ(P) have also been calculated for HCP and NP at the CCSD(T) level of theory.

The microwave spectrum of HGeCl

The J = 1 01–0 00 and 2 02–1 01 transitions of nine isotopomers of chlorogermylene, H 74Ge 35Cl, H 74Ge 37Cl, H 72Ge 35Cl, H 72Ge 37Cl, H 70Ge 35Cl, H 70Ge 37Cl, H 76Ge 35Cl, H 76Ge 37Cl, and H 73Ge 35Cl are measured at 8–9 and 16–18 GHz. The effective rotational constants, the nuclear quadrupole coupling constants of 35Cl, 37Cl, and 73Ge, and the nuclear spin-rotation coupling constants of 35Cl and 37Cl are determined.

The microwave spectrum of cyanophosphine, H 2PCN

The rotational spectra of cyanophosphine, H 2PCN, have been measured between 10 and 42.5 GHz by Fourier transform microwave spectroscopy. The rotational constants, centrifugal distortion constants, the 14N quadrupole coupling constant, and the nuclear spin–rotation coupling constants of 31P have been determined. Density functional ab initio calculations were performed, and the calculated values of the molecular constants are in excellent agreement with our experimentally determined results. The spectra of three isotopomers were measured, H 2P 12C 14N, H 2P 13C 14N, and H 2P 12C 15N. The derived r 0 structure is quite comparable to the ab initio predicted H 2PCN equilibrium geometry.

Ab initio study of the ground state properties of molecular oxygen

The electric and magnetic properties of the ground state of oxygen molecule are calculated by multiconfiguration self-consisted field (MCSCF) method and compared with experimental data: the quadrupole moment, polarizability, the 17 O nuclear quadrupole coupling constant, magnetizability tensor, nuclear spin–rotation coupling constant and rotational g factor. The last two constants are calculated for all possible isotope modifications. The rotational, ESR and NMR spectra are discussed. Fermi-contact hyperfine coupling parameter is additionally estimated by different methods. The NMR chemical shielding tensor for 17 O 16 O species at high temperature limit (without electron spin contribution) is predicted. Potential energy curves for 10 excited bound states and the internuclear distance dependence of the studied properties are also presented.

The molecular properties of chlorosyl fluoride, FClO, as determined from the ground-state rotational spectrum

The pure rotational spectrum of chlorosyl fluoride was studied by microwave Fourier transform spectroscopy and conventional millimeter and submillimeter absorption spectroscopy. More than 100 rotational transitions for each isotopomer were observed involving J⩽73, 61 and Ka⩽19, 16 for F35ClO and F37ClO, respectively. The analysis yielded precise rotational, centrifugal distortion, Cl35,37 nuclear quadrupole, and F19 and Cl35,37 nuclear spin–rotation coupling constants. The spin–rotation constants were used to derive nuclear magnetic shielding values. All nonzero elements of the Cl quadrupole tensor were obtained, permitting its diagonalization. The dipole moment was determined by Stark measurements in the millimeter region. The ground-state average structure rz and an estimate of the equilibrium structure re were calculated. The properties derived for FClO were compared with those of ClF3 and other related molecules. Structural parameters, harmonic force constants, the dipole moment, and the nuclear quadrupole coupling constants were also evaluated by means of quantum-chemical calculations. The results are in good agreement with experiment.

Microwave spectra, geometries, and hyperfine constants of OCCuX (X = F, Cl, Br).

A pulsed jet cavity Fourier transform microwave spectrometer has been used to measure the rotational spectra of OCCuX (X = F, Cl, Br) in the frequency range 5-21 GHz. Metal atoms were generated via laser ablation and were allowed to react with CO and a halide precursor, prior to stabilization of the products within a supersonic jet. These are the first experimental observations of OCCuF and OCCuBr and the first high-resolution spectroscopic study of gas-phase OCCuCl. All three molecules were found to be linear. Rotational constants, centrifugal distortion constants, nuclear quadrupole coupling constants, and nuclear spin-rotation coupling constants have been precisely determined. The rotational constants have been used to evaluate the various bond lengths, and the results are in good agreement with the trend established for OCAuX species. The C-O distance is found to be comparatively short and close to that of free CO. The M-C distance is longer than that predicted by ab initio calculations, and the Cu-X distances are very similar to those observed in the corresponding metal halides. Vibrational wavenumbers have been estimated from the distortion constants and are compared with the results of various ab initio studies. Changes in the Cu, Cl, and Br nuclear quadrupole coupling constants indicate that substantial charge rearrangement takes place on coordination with CO, consistent with the formation of strong Cu-C bonds. Mulliken orbital population analyses have been performed and provide evidence of pi-back-donation from Cu in all of the species studied. The evaluated nuclear spin-rotation coupling constants have been used to estimate the (63)Cu nuclear shielding constants, sigma, and their spans (Omega) in OC(63)CuF, OC(63)Cu(35)Cl, and OC(63)Cu(79)Br.

The rotational spectrum of chlorine trifluoride, ClF3. Centrifugal distortion analysis, Cl nuclear magnetic shielding tensor, structure, and the harmonic force field

The rotational spectrum of the T-shaped ClF3 was recorded for both 35Cl and 37Cl isotopomers in selected regions between 66 and 581 GHz. The observation of transitions involving J and Ka quantum numbers of up to 82 and 27, respectively, permitted the first centrifugal distortion analysis for this molecule. The quartic distortion constants were used together with data for the fundamental vibrations to derive harmonic force constants which were also calculated by means of ab initio methods. The harmonic force field and the rotational constants were employed to obtain ground state average (rz) structural parameters and to estimate the equilibrium structure (re). Most of the rotational transitions showed resolved hyperfine splitting due to the 35Cl or 37Cl nucleus yielding, under consideration of previous data, accurate quadrupole coupling constants and, for the first time, nuclear spin–rotation coupling constants. While the former have been interpreted in terms of ionic bonding of the two different ClF bonds comparable to that in the ClF molecule, the latter were used to calculate nuclear magnetic shielding tensors.

MCSCF response calculations of the excited states properties of the O2 molecule and a part of its spectrum

A number of transitions including the triplet–singlet band f′1Σu+←X3Σg−, have been studied by ab initio multi-configurational self-consistent field (MCSCF) response methods. Potential energy curves for eight excited states obtained by linear response calculation are in a good agreement with recent experimental data and exhibit some new findings. Quadrupole moments for the 12 lowest states have been calculated which can be used for intermolecular interaction analysis and solvent shift estimations. The nuclear quadrupole coupling constant, magnetizability tensor, nuclear spin–rotation coupling constant and rotational g-factor are also presented. For the three lowest singlet states these parameters are analyzed in detail.

The Rotational Spectrum of SO2 and the Determination of the Hyperfine Constants and Nuclear Magnetic Shielding Tensors of 33SO2 and SO17O

Precise frequencies for the 111–202 transition of 33SO2 and SO17O in natural isotopic abundance have been obtained near 12 GHz by microwave Fourier transform spectroscopy in order to yield improved hyperfine constants. Nuclear spin–rotation coupling constants have been determined experimentally for 33SO2 for the first time. The spin–rotation constants have been used to derive nuclear magnetic shielding parameters. These parameters are compared with values for the isoelectronic O3 molecule. The transition mentioned above was also measured for 32SO2, 34SO2, SO18O, and vibrationally excited (v2 = 1) 32SO2. For 33SO2, some transitions with large hyperfine splitting were also recorded in the millimeter-wave region. Continuing our investigations of the rotational spectra of SO2 in the submillimeter region, several transitions of SO17O have been recorded with the Cologne terahertz spectrometer between 540 and 840 GHz with J and Ka up to 63 and 16, respectively. Transitions with high Ka, up to 28, have been recorded with the JPL laser sideband spectrometer between 1.8 and 3.2 THz.

Sub-Doppler Measurements of the Rotational Spectrum of 13C16O

The five lowest J rotational transitions of 13C16O have been measured by saturation-dip spectroscopy to an accuracy of about 2 kHz, employing phase-stabilized backward-wave oscillators (BWOs). These highly precise measurements cover the transitions from J = 2 ← 1 to J = 6 ← 5 with frequencies ranging from 220 to 661 GHz. For each of the five observed rotational transitions, the narrow linewidths of the saturation dips (about 20 kHz) permitted the resolution of the hyperfine splitting for the first time. This splitting is caused by the 13C-nuclear spin–rotation interaction yielding a value for the nuclear spin–rotation coupling constant of CI(13C16O). If combined with the beam measurements (CI(13C16O) = 32.63(10) kHz), a slight J-dependence of the spin–rotation coupling constant can be determined (CJ = 30 ± 13 Hz). In addition, we have measured in the Doppler-limited mode several higher J rotational line positions of 13C16O up to 991 GHz with an accuracy of 5 kHz. The two line positions (J = 12 ← 11 and J = 14 ← 13) were recorded by multiplying BWO frequency with an accuracy of 100 kHz. The rotational transitions J = 17 ← 16 and J = 18 ← 17 were measured with an accuracy between 15 and 25 kHz by using the Cologne sideband spectrometer for terahertz applications COSSTA.

Ab initio nuclear shielding parameters and spin-rotation coupling constants of FBO, ClBO and FBS

Ab initio nuclear shielding parameters and nuclear spin-rotation coupling constants of FBO, ClBO and FBS have been calculated using the multi-configuration self consistent field (MCSCF) method. The dependence of these parameters upon the basis set and active space employed in the calculation was investigated. The results are compared with the experimental values obtained from microwave spectra.