The electronic structure of the mixed 5f system UC x N1−x

We present results of electronic structure calculations for UC _x N_1–x obtained with the relativistic Korringa-Kohn-Rostocker Greens function (RKKR-GF) method. While on the anion sites the disorder is treated within the Coherent Potential Approximation (CPA) the small change in the cation potential upon alloying is accounted for in the averaget-matrix approximation (ATA). The presence of strong local spin fluctuations forx0.6 restricts our treatment to the carbon rich phase, and even there we find that the observed linear specific heat coefficient is much enhanced over the bandstructure value. The computed X-ray photoemission spectra vary smoothly with composition the main change consisting in the melting away of the side peak at –3 eV binding energy seen in pure UC with the adjunction of nitrogen.     

Inferring unresolved hyperfine structure in liquid solution EPR:14N hyperfine structure in the 1∶1 copper-calcimycin complex

Theoretical expressions for EPR line widths in liquids suggest the following two strategies for inferring unresolved hyperfine structure in near square planar copper(II) complexes and thereby identify the coordinating ligand atoms: (i) Increasing the resolution by reducing the line widths, by forming a mixed ligand complex of lower magnetic anisotropy. (ii) By demanding that the magnetic anisotropy determined from line widths, assuming unresolved hyperfine structure, should agree with that determined from frozen solution EPR spectrum.¹⁴N hyperfine structure from a coordinating cal (A _N ～ 12 G) in 1∶1 copper-calcimycin complex (Cu?cal) has been observed / inferred by the application of these strategies in 1∶1 chloroform-ethanol mixtures. It has been suggested that Cu?cal prepared in the presence of the bidentate ligand diethyldithiocarbamate (dtc^?) is the mixed ligand complex Cu(dtc)(cal) in which cal is a bidentate ligand. The Cu?cal prepared in the presence of a monodentate anion AN (AN=NO ₃ ^? , Br^?, Cl^? etc.) is Cu(AN)(cal) in which cal is a tridentate ligand. These complexes have near planar coordination geometry.     

Rotational structure of the origin band in the 1A′ ←X1σ+ electronic transition of C4H− and C4D−

The rotational structure of the origin band for the ¹A′←X¹σt⁺ electronic transition, lying just below the electron affinity of C⁴H, was recorded by means of a two-colour resonant photodetachment technique. This allowed a determination of the rotational constants in the X¹σt⁺ ground and ¹A′ dipole bound excited state. The low lying A²II excited state of C⁴H is inferred to be the parent of the dipole bound state. The excited electronic state is deduced to have a nonlinear planar structure whereas the ground is linear according to the spectral analysis. The rotational constants have been obtained: B′; = 0.1552(2)cm^?1 for the X¹σt⁺ state, and A′ = 30.73(1), B′ = 0.1587(2), C′ = 0.1581(2)cm^?1 for the ¹A′ state.     

The S21 lines of the A2Σ+ (v′ = 1)←X2Π (v″ = 0) transitions of OH and OD

The S₂₁ lines of the OH radical for the A²Σ⁺ (v′ = 1)←X²Π (v″ = 0) transition have been observed in the 278–280 nm region from the laser-excitation spectrum. The OH radical was generated from either the H + NO₂ or the H + O₃ reaction in a flow system and the fluorescence passing through a 309.6 nm interference filter was detected with a photomultiplier-boxcar integrator arrangement. The weak S₂₁ lines were observed at laser energies above 0.2 mJ. The observed peak wavenumbers are in excellent agreement with those predicted for the S₂₁ bands of the A (v>′ = 1)←X (v″ = 0) transition from the known spectroscopic parameters. Observation of the corresponding S₂₁ system for OD in the 286.0–286.9 nm region further confirms this assignment. The relative absorption cross-sections of about one-tenth those of the P₁ lines are in good agreement with theoretical considerations.     

The magnetic circular dichroism spectrum of the 1 B 2u ←1 A 1g transition of benzene in the vapour phase

The magnetic circular dichroism (MCD) spectrum of the ¹ B _2u ←¹ A _1g transition of benzene has been measured in the vapour phase. Many of the bands due to transitions between single vibronic levels display A terms. It has been shown that the angular momentum arises by vibronic mixing both of the ¹ E _1u state with the ¹ B _1u state and of the ¹ E _2g states with the ¹ A _1g ground state by e _2g vibrations. The magnitudes and signs of the experimental and calculated ratios, A/D, for the A ₀ ⁰ vibronic origin are in excellent agreement. Two strong MCD progressions of opposite sign with B-term dispersion have been observed in regions of low absorption. These are identified with vibronic origins due to the v ₈ and v ₉ e _2g modes. By contrast the MCD spectrum of hexadeuterobenzene vapour has a much lower magneto-rotational strength and displays none of the striking features of the benzene MCD spectrum.     

The molecular and electronic structure of N,N′-ethylenebis(acetylacetonylideiminato)oxovanadium(IV) and the electronic structure of its thio analogue

The electronic structures of the title complexes—VO(acen) and VS(acen)—and the free H₂(acen) ligand are probed using gas-phase UV-photoelectron spectroscopy [acen = N,N′-ethylenebis(acetylacetonylideiminato)]. The effect of the different axial donors on the metal center is examined, as is the effect that the oxo and thio ligands have on the acen orbitals. We find that the oxo and thio donors primarily affect the metal center and that the ligand periphery remains mostly unchanged.     

An ab initio study of the hyperfine structure in the X2 Π electronic state of HCCS–calculation of vibronically averaged components of the anizotropic hyperfine tensor

The results of ab initio calculations of the vibronically averaged components of the anisotropic magnetic hyperfine tensor in the low-lying vibronic species of the X²Π electronic state of the HCCS radical are reported. The electronically averaged hyperfine coupling constants for hydrogen, deuterium, ¹³C and ³³S are obtained as functions of two bending vibrational modes by the density functional theory method. The vibronic wave functions are calculated with the help of a variational approach which takes into account the Renner–Teller effect and spin-orbit coupling. The results of ab initio calculations are compared to the corresponding experimental findings.     

Theoretical investigation of the Renner-Teller effect in Δ electronic states of tetra-atomic molecules. 1. Variational calculation of vibronic structure in the 11Δg state of B2H2

A variational approach for the ab initio handling of the Renner-Teller effect in Δ electronic states of tetra-atomic molecules is presented. The model Hamiltonian involves four nuclear degrees of freedom which correlate for a linear nuclear arrangement with two doubly degenerate bending modes. The bond lengths are assumed to be kept fixed at their equilibrium values and the effect of end-over-end rotations is neglected. The kinetic energy operator and the general form of the potential surfaces employed allow in principle for a treatment of large amplitude bending vibrations. However, because of restrictions implied, such as neglect of coupling between bending and stretching vibrations and interactions with other electronic states, the approach is aimed primarily at molecules bending with relatively small amplitudes around their linear equilibrium geometries. Two algorithms are developed, one for symmetric acetylene-like (A-B-B-A) molecules, the other for asymmetric (A-B-C-D) species. The approach is applied to calculate the vibronic spectrum of the lowest lying excited state, ¹Δ_g, of B₂H₂, employing ab initio computed potential energy surfaces.     

Reinvestigation of the high spin states in 《'161》Er and enhanced E1 transitions in the N=93 isotones

High-spin states in <'161>Er have been studied experimentally using the <'150>Nd(<'16>O, 5n) reaction at a beam energy of 86 MeV. The relatively enhanced E1 transitions between the 5/2<'+> [642] and 3/2<'-> [521] bands are observed in <'161>Er, and the B(E1) values are extracted experimentally. The systematics of the R(E1) values in the N = 93 isotones are presented. It is found that the strength of the E1 transitions obviously exhibits angular momentum dependence, and the occurrence of the relatively enhanced E1 transitions could be attributed to octupole softness.     

Reinvestigation of the high spin states in ^（161）Er and enhanced E1 transitions in the N=93 isotones

High-spin states in ¹⁶¹Er have been studied experimentally using the ¹⁵⁰Nd(¹⁶O, 5n) reaction at a beam energy of 86 MeV. The relatively enhanced E1 transitions between the 5/2⁺[642] and 3/2^-[521] bands are observed in ¹⁶¹Er, and the B(E1) values are extracted experimentally. The systematics of the R(E1) values in the N=93 isotones are presented. It is found that the strength of the E1 transitions obviously exhibits angular momentum dependence, and the occurrence of the relatively enhanced E1 transitions could be attributed to octupole softness.     

High-resolution laser spectroscopy of CaNH2: Analysis of the C̃2A1-X̃2A1 system

Laser excitation spectra of the $\text{C}\text{?}{}^2\text{A}{}_1\text{-}\text{X}\text{?}{}^2\text{A}{}_1$ system of CaNH₂ are reported. Due to the spectral density, individual lines could only be resolved and measured using a filtered fluorescence excitation technique, with a monochromator acting as an optical bandpass filter; 140 line positions were measured in this way and assigned to the parallel K_?1 = 1 subband of what is believed to be the vibrational 0-0 band. The molecular constants were determined from a weighted nonlinear least-squares fit of the line positions.

     

12.

The effect of frenkel defects on the electronic structure of 1T−TiSe2     

E. Pehlke  W. Schattke 《Zeitschrift für Physik B Condensed Matter》1987,66(1):31-37

Using a tight binding formalism the wave vector resolved electronic density of states has been calculated in the coherent potential approximation for an 1 T–TiSe₂ crystal containing Frenkel defects. Additional structure originating from disorder is discussed. An extra peak in the A direction at 1.5 eV binding energy can be traced back to a resonance caused by titanium vacancies.     

13.

Profiles of (υ′;υ″ = 0) bands recorded in excitation spectra using b30+u ← X10g+ transitions in Cd2 and B31 ← X10+ transitions in CdAr     

T. Urbanczyk 《Molecular physics》2014,112(18):2486-2494

Profiles of the (υ′;υ ^″ = 0) vibrational bands recorded using the b³0⁺ _u ← X¹0_g ⁺ and B³1?←?X¹0⁺ transitions in Cd₂ and CdAr complexes, respectively, are presented and analysed. Specifically, CdAr and Cd₂ complexes are simultaneously propagating in a supersonic beam. Transitions in these complexes can be used to provide the conditions for selective detection of one of the complexes in the expansion. Extended analysis of the B³1- and b³0⁺ _u -state vibrational progressions provided improved values for ω′ _e x′ _e and ω′ _e vibrational characteristics, as well as D′ _e well depths and R _e ′ bond lengths of the B³1- and b³0⁺ _u-state potentials. Several of the CdAr bands were recorded with partly resolved rotational structure. The new characterisation of the B³1 state, along with results of the rotational and isotopic analyses of the band profiles, agrees with the most recent results of ab initio calculations, while results obtained for the b³0⁺ _u state call for improvement in the ab initio calculations for Cd₂.     

14.

The B̃2Σ−g (Πu) ← X̃2A1 system of nitrogen dioxide in neon matrices     

H.D. Bist  J.C.D. Brand  A.R. Hoy  V.T. Jones  R.J. Pirkle 《Journal of Molecular Spectroscopy》1977,66(3):411-420

The $\text{B}\text{?}\text{←}\text{X}\text{?}$ band system of NO₂, ${}^2\text{Σ}{}^{\mathrm{?}}{}_{\mathrm{g}}\text{(π}{}_{\mathrm{u}}\text{) ←}{}^2\text{A}{}_1$, has been measured in absorption in a neon matrix at 6 K, using ¹⁵NO₂ and N¹⁸O₂ in addition to the normal isotope. The spectrum consists essentially of a single, long progression of bands terminating on successive levels of the bending mode in the upper state. Transitions to odd- and even-v₂′ states occur with a uniform intensity distribution indicating that the rotation of the bent ground state of NO₂ about its near-prolate axis is hindered in the matrix. The observations strongly suggest that the top axis of the molecule coincides with a C₂ axis of neon crystals in the polycrystalline matrix. Relative to the vapor absorption the matrix spectrum is red shifted by about 150 cm^?1, the crystal field parameter V₂ and principal constants of the $\text{B}\text{?}$ state of ¹⁴N¹⁶O₂ in neon being

$\text{T}{}_{010}\text{14 571 cm}{}^{\mathrm{?1}}\text{: x}{}_{22}\text{, ?0.3 cm}{}^{\mathrm{?1}}\text{;}$

$\text{w}{}_2\text{460.2 cm}{}^{\mathrm{?1}}\text{: V}{}_2\text{, 80 cm}{}^{\mathrm{?1}}\text{.}$

     

15.

Ab initio CI study of the vibrational structure of the 1 1Σ− (1 1 A″)←X and 1 1Δ (2 1 A′, 2 1 A″)←X electronic transitions in HCN and DCN     

M. Perić  R.J. Buenker  S.D. Peyerimhoff 《Molecular physics》2013,111(5):843-864

The results of an ab initio CI study of the vibrational/vibronic structure of the 1 ¹Σ^? (1 ¹ A″)←X and 1 ¹Δ (2 ¹ A′, 2 ¹ A″)←X electronic transitions in HCN and DCN are presented. Calculated band positions and intensity distributions within the band progressions are compared with corresponding experimental data. While the theoretical results for the 1A″←X transition reproduce well the structure of the observed A-X spectrum, they place doubt on the Bickel-Innes interpretation of the B-X band system in terms of transitions to the same excited electronic state but accompanied by excitation of a single quantum of the C?H stretching vibrational mode.     

16.

Semiclassical calculations of half-widths and line shifts for transitions in the 30012←00001 and 30013←00001 bands of CO2, I: Collisions with N2     

Robert R. Gamache  Julien Lamouroux  Anne L. Laraia  Jean-Michel Hartmann  Christian Boulet 《Journal of Quantitative Spectroscopy & Radiative Transfer》2012,113(11):976-990

Calculations of the half-width, its temperature dependence, and the line shift are made for the rotational states J=0–120 for two of the Fermi-tetrad bands (30012←00001 and 30013←00001) of CO₂ perturbed by N₂. The calculations employ the semi-classical complex Robert–Bonamy method with no ad hoc scaling, J-dependent or otherwise, and an intermolecular potential (IP) comprised of an electrostatic part, an atom–atom part, and an isotropic London dispersion part. The averaging over the impact parameter b and relative speed v are explicitly carried out. Many interesting features about CO₂ as the radiating molecule are elucidated. Effects of the trajectory model, the order of the expansion of the atom–atom component of the potential, and the inclusion of the imaginary terms are studied. It is shown that the results are very sensitive to the intermolecular potential. The final IP parameters give results that demonstrate excellent agreement with measurement for the three line shape parameters studied in this work.     

17.

The Renner–Teller effect observed in the and electronic states of H2S+     

G. Duxbury  Ch. Jungen  A. Alijah  J.P. Maier  D. Klapstein 《Molecular physics》2014,112(23):3072-3084

     

18.

Coupled ab initio potential energy surfaces for the two lowest 2A′ electronic states of the C2H molecule     

M. BOGGIO-PASQUA  A. I. VORONIN  PH. HALVICK  J.-C. RAYEZ  A. J. C. VARANDAS 《Molecular physics》2013,111(23):1925-1938

Realistic two-valued potential energy surfaces for the reaction C(³P) + CH(X²Π) → C₂ + H have been constructed from a set of high level ab initio data describing the first two ²A′ electronic states of the C₂H system. These states have linear equilibrium configurations, known as the X ²Σ⁺ and A²Π states, and are coupled by a conical intersection. They lead to the formation of C₂(X¹Σ⁺ _g) and C₂(a³Π_u) considering an adiabatic dissociation process. The ab initio calculations are of the multireference configuration interaction variety and were carried out using a polarized triple-zeta basis set. Using the ab initio adiabatic energies and the matrix elements of the dipole moment, a 2 × 2 diabatic representation of the electronic Hamiltonian was built. Each element of this Hamiltonian matrix was expressed within the double many-body expansion (DMBE) scheme which is based, in this case, on the extended Hartree-Fock approximate correlation energy model (EHFACE). The analytical adiabatic potential energy surfaces are then obtained as the eigenvalues of this matrix, and display correctly the Σ/Π conical intersection. Moreover, the non-adiabatic couplings given by our analytical model are compared with the ab initio ones, and good qualitative agreement is observed.     

19.

Theoretical study of the Renner-Teller A 2A1 − X 2B1 system of NH2     

W. GABRIEL  G. CHAMBAUD  P. ROSMUS  S. CARTER  N. C. HANDY 《Molecular physics》2013,111(12)

(Molec. Phys., 1994, 81, 1445–1461)     

20.

Analysis of perturbations in the B2Σ+-X2Σ+ system of SrBr     

《Journal of Molecular Spectroscopy》1986,117(2):444-447

     

		Main parameters
	$\text{X}\text{?}{}^2\text{A}{}_1$	$\text{C}\text{?}{}^2\text{A}{}_1$
$\text{T}{}_{\mathrm{k?1}}\text{= 1}$	3-	17375.129(5)
B	0.30079(6)	0.30562(6)
C	0.29319(6)	0.29789(8)
$\text{?}{}_{\mathrm{aa}}$	3-	?0.66(4)
$\text{?}{}_{\mathrm{bb}}$	3-	?0.0356(8)
$\text{?}{}_{\mathrm{cc}}$	3-	?0.0453(8)

The effect of frenkel defects on the electronic structure of 1T−TiSe2

Using a tight binding formalism the wave vector resolved electronic density of states has been calculated in the coherent potential approximation for an 1 T–TiSe₂ crystal containing Frenkel defects. Additional structure originating from disorder is discussed. An extra peak in the A direction at 1.5 eV binding energy can be traced back to a resonance caused by titanium vacancies.     

Profiles of (υ′;υ″ = 0) bands recorded in excitation spectra using b30+u ← X10g+ transitions in Cd2 and B31 ← X10+ transitions in CdAr

Profiles of the (υ′;υ ^″ = 0) vibrational bands recorded using the b³0⁺ _u ← X¹0_g ⁺ and B³1?←?X¹0⁺ transitions in Cd₂ and CdAr complexes, respectively, are presented and analysed. Specifically, CdAr and Cd₂ complexes are simultaneously propagating in a supersonic beam. Transitions in these complexes can be used to provide the conditions for selective detection of one of the complexes in the expansion. Extended analysis of the B³1- and b³0⁺ _u -state vibrational progressions provided improved values for ω′ _e x′ _e and ω′ _e vibrational characteristics, as well as D′ _e well depths and R _e ′ bond lengths of the B³1- and b³0⁺ _u-state potentials. Several of the CdAr bands were recorded with partly resolved rotational structure. The new characterisation of the B³1 state, along with results of the rotational and isotopic analyses of the band profiles, agrees with the most recent results of ab initio calculations, while results obtained for the b³0⁺ _u state call for improvement in the ab initio calculations for Cd₂.     

The B̃2Σ−g (Πu) ← X̃2A1 system of nitrogen dioxide in neon matrices

The $\text{B}\text{?}\text{←}\text{X}\text{?}$ band system of NO₂, ${}^2\text{Σ}{}^{\mathrm{?}}{}_{\mathrm{g}}\text{(π}{}_{\mathrm{u}}\text{) ←}{}^2\text{A}{}_1$, has been measured in absorption in a neon matrix at 6 K, using ¹⁵NO₂ and N¹⁸O₂ in addition to the normal isotope. The spectrum consists essentially of a single, long progression of bands terminating on successive levels of the bending mode in the upper state. Transitions to odd- and even-v₂′ states occur with a uniform intensity distribution indicating that the rotation of the bent ground state of NO₂ about its near-prolate axis is hindered in the matrix. The observations strongly suggest that the top axis of the molecule coincides with a C₂ axis of neon crystals in the polycrystalline matrix. Relative to the vapor absorption the matrix spectrum is red shifted by about 150 cm^?1, the crystal field parameter V₂ and principal constants of the $\text{B}\text{?}$ state of ¹⁴N¹⁶O₂ in neon being

$\text{T}{}_{010}\text{14 571 cm}{}^{\mathrm{?1}}\text{: x}{}_{22}\text{, ?0.3 cm}{}^{\mathrm{?1}}\text{;}$

$\text{w}{}_2\text{460.2 cm}{}^{\mathrm{?1}}\text{: V}{}_2\text{, 80 cm}{}^{\mathrm{?1}}\text{.}$

     

Ab initio CI study of the vibrational structure of the 1 1Σ− (1 1 A″)←X and 1 1Δ (2 1 A′, 2 1 A″)←X electronic transitions in HCN and DCN

The results of an ab initio CI study of the vibrational/vibronic structure of the 1 ¹Σ^? (1 ¹ A″)←X and 1 ¹Δ (2 ¹ A′, 2 ¹ A″)←X electronic transitions in HCN and DCN are presented. Calculated band positions and intensity distributions within the band progressions are compared with corresponding experimental data. While the theoretical results for the 1A″←X transition reproduce well the structure of the observed A-X spectrum, they place doubt on the Bickel-Innes interpretation of the B-X band system in terms of transitions to the same excited electronic state but accompanied by excitation of a single quantum of the C?H stretching vibrational mode.     

Semiclassical calculations of half-widths and line shifts for transitions in the 30012←00001 and 30013←00001 bands of CO2, I: Collisions with N2

Calculations of the half-width, its temperature dependence, and the line shift are made for the rotational states J=0–120 for two of the Fermi-tetrad bands (30012←00001 and 30013←00001) of CO₂ perturbed by N₂. The calculations employ the semi-classical complex Robert–Bonamy method with no ad hoc scaling, J-dependent or otherwise, and an intermolecular potential (IP) comprised of an electrostatic part, an atom–atom part, and an isotropic London dispersion part. The averaging over the impact parameter b and relative speed v are explicitly carried out. Many interesting features about CO₂ as the radiating molecule are elucidated. Effects of the trajectory model, the order of the expansion of the atom–atom component of the potential, and the inclusion of the imaginary terms are studied. It is shown that the results are very sensitive to the intermolecular potential. The final IP parameters give results that demonstrate excellent agreement with measurement for the three line shape parameters studied in this work.     

Coupled ab initio potential energy surfaces for the two lowest 2A′ electronic states of the C2H molecule

Realistic two-valued potential energy surfaces for the reaction C(³P) + CH(X²Π) → C₂ + H have been constructed from a set of high level ab initio data describing the first two ²A′ electronic states of the C₂H system. These states have linear equilibrium configurations, known as the X ²Σ⁺ and A²Π states, and are coupled by a conical intersection. They lead to the formation of C₂(X¹Σ⁺ _g) and C₂(a³Π_u) considering an adiabatic dissociation process. The ab initio calculations are of the multireference configuration interaction variety and were carried out using a polarized triple-zeta basis set. Using the ab initio adiabatic energies and the matrix elements of the dipole moment, a 2 × 2 diabatic representation of the electronic Hamiltonian was built. Each element of this Hamiltonian matrix was expressed within the double many-body expansion (DMBE) scheme which is based, in this case, on the extended Hartree-Fock approximate correlation energy model (EHFACE). The analytical adiabatic potential energy surfaces are then obtained as the eigenvalues of this matrix, and display correctly the Σ/Π conical intersection. Moreover, the non-adiabatic couplings given by our analytical model are compared with the ab initio ones, and good qualitative agreement is observed.     

Theoretical study of the Renner-Teller A 2A1 − X 2B1 system of NH2

(Molec. Phys., 1994, 81, 1445–1461)