Ab initio study of low-lying electronic states of the PF2 radical

The equilibrium geometries, excitation energies, force constants, and vibrational frequencies of the low-lying electronic states X²B₁, ²A₁, ²B₂, and ²A₂ of the PF₂ radical have been calculated at the MRSDCI level with a double zeta plus polarization basis set. Our calculated geometry, force constants, and vibrational frequencies for the X²B₁ state are in good agreement with experimental data. The electronic transition moments, oscillator strengths for the ²A₁ → X²B₁ and ²A₂ → X²B₁ transitions, and radiative lifetimes for the ²A₁ and ²A₂ states are calculated based on the MRSDCI wave functions. © 1994 by John Wiley & Sons, Inc.     

Ab initio study of the low-lying electronic states of the CH2NO2 radical

Ab initio electronic structures calculations are reported for the four low-lying electronic states X ²B₁, ²B₂, ²A₂, and ²A₁ of the CH₂NO₂ radical. The geometric parameters for the ground-state X ²B₁ are predicted by MRSDCI calculations with a double zeta plus polarization basis set. The vertical excitations energies for these electronic states are determined using MRSDCI /DZ +P calculations at the ground-state equilibrium geometry and in agreement with the recent experimental data obtained via PES of the CH₂NO anion. The oscillator strenghts and the radiative lifetimes for these electronic states and the spin properties for the ground state are calculated based on the MRSDCI wave functions, predicting results in good agreement with available experimental data. © 1994 John Wiley & Sons, Inc.     

The MRSDCI studies of four low-lying electronic states of the BF2 radical

The equilibrium geometries, excitation energies, force constants, and vibrational frequencies for four low-lying electronic states X ²A₁, ²B₁, ²B₂, and ²A₂ of the BF₂ radical have been calculated at the MRSDCI level with a double zeta plus polarization basis set. Our calculated excitation energy for X²A₁ → ²B₁ is in agreement with available experimental data. The electronic transition dipole moments, oscillator strengths for the ²B₁ → X²A₁ and ²B₂ → X²A₁ transitions, radiative lifetimes for the ²B₁ and ²B₂ states, and the spin properties for the X²A₁ state are calculated based on the MRSDCI wave functions, predicting results in reasonable agreement with available experimental data. © 1993 John Wiley & Sons, Inc.     

A restricted active space (RAS) SCF study of the lifetime of theA 3Π state of OH+

Summary Restricted Active Space (RAS) SCF calculations have been performed of the potential curves for theX ^3– andA ³ states of the OH⁺ ion and on the lifetime of thev=0–2 vibrational levels of theA state. The convergence of the transition moment integral as a function of the size of the active orbital space was used to select the active orbitals. The calculated value of thev=0 lifetime is 2.4 µs. An estimate of the errors remaining in the calculation leads to a final theoretical value of 2.7±0.1 µs. Computed bond distances and bond energies are 1.031 (1.029) Å and 5.05 (5.01) eV, respectively, for theX state, and 1.137 (1.135) Å and 1.57 eV, respectively, for theA state (experimental values within parenthesis).On leave from Departamento de Quimica Fisica, Universitat de València, Dr. Moliner 50, Burjassot, 46 100 València, Spain     

Ab initio CI study of the nitric oxide dimer (N2O2)

Configuration interaction (CI) studies of the ground and electronically excited states are reported for nitric oxide dimer (N₂O₂) in itscis equilibrium geometry. The lowest triplet state (³ B ₂) is found to lie only 0.43 eV above the ground state (¹ A ₁). The¹ A ₁ ¹ B ₁ transition is shown to be responsible for the rising absorption in the near infrared region observed experimentally. The transition of¹ A ₁¹ A ₂ calculated in the visible spectrum range of 701 nm (1.77 eV) is symmetry forbidden.     

Ab initio calculations on small hydrides including electron correlation

The two lowest electronic states (³ B ₁ and ¹ A ₁) of the methylene radical (CH₂) are calculated both in SCF-approximation and with the IEPA-PNO method (including electron correlation). The influence of polarization functions and electronic correlation on the shape of the potential curves of the two states is discussed. The calculated equilibrium geometries agree very well with experiment, but the results for transition energies (e.g. ³ B ₁¹ A ₁ excitation energy=9.2 kcal/mole, total binding energy=187 kcal/mole) are more reliable than the existent experimental values.     

Ab initio study of low-lying electronic states of the FNO2 molecule

Ab initio electronic structure calculations are reported for low-lying electronic states, ¹A₁, ¹A₂, ³A₂, ¹B₁, ³B₁, ¹B₂, and ³B₂ of the FNO₂ molecule. Geometric parameters for the ground state ¹A₁ are predicted by MRSDCI calculations with a double-zeta plus polarization basis set. The vertical excitation energies for these electronic states are determined using MRSDCI/DZ+P calculations at the ground-state equilibrium conformation. The oscillator strengths and radiative lifetimes for some electronic states are calculated based on the MRSDCI wave functions. © 1993 John Wiley & Sons, Inc.     

Intensités des Transitions Électroniques de [PdCl4]2− Intensities of Electronic Transitions of [PdCl4]2−

The oscillator strengths of the symmetry-forbidden transitions of the ion [PdCl₄]^2– were calculated by a method based on the evaluation of the MO of the distorted ion. It is not very likely that the transition to¹ B _1g (a _1g (d _z ²)b _1g ) state, weak, mainlyz polarized, explains the band that appears as a shoulder observed towards 30 000 cm^–1 in the absorption spectrum. If this band is specific of the ion [PdCl₄]^2–, the assignment to the forbidden charge-transfer transition,¹ A _1g ¹ B _2g , is more plausible.

     

Structure,vibrational spectra,and energetic stability of LnX<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack> ions (Ln=La,Lu; X=F,Cl, Br,I)

Molecular structure and properties of La and Lu tetrahalide ions LnX ₄ ^– ) are studied by the configuration interaction singles-and-doubles method augmented with quadruple excitation correction (CISD+Q) and by the fourth-order Möller-Plesset perturbation theory with account for single, double, triple, and quadruple excitations (SDTQ-MP4). The atomic inner shells are described by Stevens relativistic effective core potentials. Valence basis sets are augmented with diffuse s-, p-, and polarization d-, f-, and g-functions. The equilibrium configuration of nuclei in LnX ₄ ^– ions was found to be tetrahedral. The equilibrium internuclear distances, quadratic force constants, vibrational frequencies, and IR intensities of LnX ₄ ^– ions are compared with the corresponding parameters of La and Lu trihalide molecules (LnX₃), calculated within the same approximations. Regularities in the behavior of molecular parameters on going along the LnF ₄ ^– LnCl ₄ ^– LnBr ₄ ^– LnI ₄ ^– series and from La compounds to Lu compounds are revealed. Heights of the energy barriers to the LnX ₄ ^– inversion through the square planar structures (T _d D _4h T _d ) are evaluated: 100–110 and 130–150 kJ/mol for LaX ₄ ^– and LuX ₄ ^– , respectively. Enthalpies of dissociation reactions LnX ₄ ^– LnX₃+X^– are calculated and the results obtained are compared with the available experimental data.Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 3, 2005, pp. 218–228.Original Russian Text Copyright © 2005 by Solomonik, Smirnov, Mileyev.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Vibronic spectral behavior of molecules: XVIII. Theoretical contribution to the S1→S0 fluorescence of the isomeric phenyl naphthalenes within the Herzberg-Teller approach

Theoretical vibronic S₁S₀ line spectra of the isomeric phenyl naphthalenes calculated within the Condon as well as the Herzberg-Teller approaches on the basis of completely optimizedS ₀ andS ₁ molecular geometries, are presented and are contrasted with the experimental fluorescence spectra. The theory-experiment comparison is successful only within the Herzberg-Teller approximation by explicitly including the Dushinsky transformation. An analysis of the significant vibrational modes is given.     

Kinetics of formation of sulfur dimers in pure SF6 and SF6-O2 discharges

The emission band spectra of S, molecule (B³ _u ^– X³ _g ^– transition) and of SO molecule (A³ X^3–) were detected in SF₆ and SF₆-O₂ rf discharges. It has been observed that the presence of a material which can be etched by SF₆ products considerably enhances the density of S₂ in the reactor. By means of mass spectrometry it has been shown that the m/e =83 mu signal assigned to S₂F⁴ ions evolves exactly in the same manner as the S₂ band intensity during the etching of Si or W in SF₆-O₂ discharge. A reaction scheme involving S₂F radicals is proposed to explain these experimental results.     

UV/Vis-spektroskopische Untersuchungen an Cyclosilanderivaten

UV/Vis-spectra of Cyclosilanes (SiX ₂) _n withX=Cl, Br, I, OMe andn=4, 5, 6 are recorded and interpreted qualitatively. The spectra exhibit increasing influence of the substituents on the Si-Si-bond system within the rings in the order Cl OMe Br I. At the low energy side of the spectra weak absorption bands, possibly due to intramolecular charge transfer transitions, appear. The strong inductive effect of the electronegative substituents is documented by a marked increase of the first IP's compared to permethylcyclosilanes.

     

Molybdenum complexes of biochemical iinterest. New coordination complexes of oxomolybdenum(V) with the tridentate ONO donor schiff bases derived from salicylaldehydes and ethanolamine

Summary New oxomolybdenum(V) complexes MoOCIL (where LH₂ = Schiff base) derived from ethanolamine and salicylaldehyde, 5-chlorosalicylaldehyde, 5-bromosalicylaldehyde, 5-nitrosalicylaldehyde, 3-ethoxysalicylaldehyde and 2-hydroxy-1-naphthaldehyde have been synthesized and characterised by elemental analyses, conductance, molecular weight, i.r. and electronic spectra and magnetic measurements. The Schiff bases behave as dibasic tridentate ONO donor ligands. The complexes are non-electrolytes and dimers. The complexes exhibit subnormal magnetic moments and are involved in antiferromagnetic exchange withS=0 ground state. The complexes exhibit electronic spectral bands atca. 13000 andca. 17000 cm^–1 due to the transitionsd _xy d _xz,yz (²B₂ ²E) andd _xy d _x ²–y² (²B₂ ²B₁), respectively. The (Mo=O) frequency of the complexes is observed in the 900–970 cm^–1 region. On the basis of the magnetic susceptibility, i.r. and molecular weight data a dimetallic structure with alcoholic oxygen atoms as the bridging atoms is suggested.Abbreviations sal salicylaldehyde - 5-chlorosal 5-chlorosalicylaldehyde - 5-bromosal 5-bromosalicylaldehyde - 5-nitrosal 5-nitrosalicylaldehyde - 3-ethoxysal 3-ethoxysalicylaldehyde - hydroxy 2-hydroxyl-1-naphthaldehyde     

Labelling spectroscopy on argonhydride and argondeuteride in a plasma beam penning tube

Rare gas hydride molecules and triatomic hydrogen molecules were produced in a Cossart-type plasma beam Penning tube specially designed for laser spectroscopic work. A cw dye laser was used to stimulate transitions from theB ² rovibrational levels to theA ²⁺ levels of argonhydride (⁴⁰ArH) and argondeuteride (⁴⁰ArD). The transitions were detected by measuring the decrease of the spontaneous emission from the upper levels, which clearly shows the expected population inversion between the two participating electronic states. With this first laserspectroscopic work on argonhydride and argon deuteride, the classification of the lines of theB ² A ²⁺ band as given by Johns 1970 could be checked and was found to be consistent*. Furthermore theQ branches of these bands for ArH and ArD could be completely resolved into their single lines and their wavelengths were measured. The latter allowed the difference between the rotational constants of theA andB electronic states to be directly determined. The method was also applied to triatomic hydrogen. D₃. It should be useful for classifying more complicated bands of ArH and of KrH and XeH, which can also be produced in this tube.In later theoretical work theB ² state was called 2² state [13] andE ² state [12], respectively     

Ab initio calculations of vibronic activity in phosphorescence microwave double resonance spectra of p-dichlorobenzene

The phosphorescence spectrum of p-dichlorobenzene has been calculated using multiconfiguration self-consistent-field wave functions and the quadratic response technique. Attention has been paid to the intensity distribution of the singlet–triplet (³B_1u¹A_g) transition through a number of vibronic subbands. The second order spin–orbit coupling (SOC) contribution to the spin splitting of the ³B_1u (^3*) state is found to be almost negligible, and the calculations therefore provide a good estimate for the zero-field splitting (ZFS) parameters based only on the electron spin–spin coupling expectation values. Nuclear quadrupole resonance constants for the different Cl isotopes are also calculated to accomplish the ZFS assignment. The electric dipole activity of the spin sublevels in the triplet–singlet transitions to the ground-state vibrational levels is estimated by calculations of derivatives using distorted geometries which are shifted from the equilibrium position along different vibrational modes. A vibrational analysis of the phosphorescence spectrum, based on the SOC-induced mixing of the singlet and triplet states calculated along different vibrational modes, provides reasonable agreement with experimental data.Acknowledgment O. R.-P. would like to thank the European MOLPROP network for support. The authors thank Alexander Baev for fruitful discussions. This work was supported by the Swedish Royal Academy of Science (KVA).     

Triterpene glycosides ofHedera canariensis IV. Structures of glycosides L-F3, L-G0, and L-Gla from the leaves of Algerian ivy

Three minor partially acetylated glycosides have been isolated from the leaves of Algerian ivy, Hedera canariensis Willd. (Araliaceae) — the previously known {3-O-[-L-rhamnopyranosyl-(12)-O--L-arabinopyranoside] 28-O-[-L-rhamnopyranosyl-(14)-O-(6-acetyl--D-glucopyranosyl)-(16)-O--D-glucopyranoside}s of oleanolic acid and of hederagenin (ciwujianoside C₄ and kizuta saponin K₁₁) and the new 3-O-[-L-rhamnopyranosyl-(12)--O-L-arabinopyranoside] 28-O-[-L-rhamnopyranosyl-(14)-O-(6-O-acetyl--D-glucopyranosyl)-(16)-O--D-glucopyranoside of echinocystic acid (glycoside L-G₀). The structures of the glycosides isolated have been established on the basis of chemical transformations and¹H and¹³C NMR spectroscopy.Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 81–86, January–February, 1999.     

Excited Π states of divinyl chalcogenides and chalcophenes

Electron transitions in divinyl chalcogenides (CH₂=CHXCH=CH₂, where X is S, Se, or Te) have been analyzed using UV absorption spectra of dialkyl and alkyl vinyl chalcogenides. The following relations for the orbital energies are found: ^* < ^* < ^* < ^* for Te and ^* < ^* < ^* < ^* for S and Se. For chalcophenes, a correlation between the energy of the excited state (E ^*) of specific symmetry, the ionization potential (I) and the electron affinity (EA) is obtained:E ^*=const+(I+EA)/2. The electron affinity of divinyl chalcogenides is estimated. The correlation between the excited ^* states of divinyl chalcogenides and chalcophenes is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 831–835, May, 1994.     

Time-dependent Hartree-Fock calculations for the excited ‘S’ states of lithium isoelectronic sequence

Time-dependent HF (RPA) calculations have been performed to estimate the transition energies and excited state wavefunctions of Li, Be⁺, B²⁺ and C³⁺ for the transitions 1s ²2s ² S 1s ² ns ² S (n = 3,4, ... 8). The excitation energies and excited state wavefunctions are extracted from the position of the poles of a linearised variational functional. The excitation energies are in excellent agreement with those obtained spectroscopically. The excited state wavefunctions are utilised to find the matrix elements of different operators and the cusp values.     

Theoretical rotational-vibrational spectra of theX 3 B 1,a 1 A 1 andb 1 B 1 states of NH 2 +

Summary The three-dimensional potential energy functions have been calculated from highly correlated multireference configuration interaction electronic wavefunctions for theX ³ B ₁,a ¹ A ₁, andb ¹ B ₁ states of the NH ₂ ⁺ ion. For the quasi-linear electronic ground state this information and the electric dipole moment functions have been used to calculate spectroscopic constants, line intensities and rotationally resolved absorption spectra. For thea ¹ A ₁-b ¹ B ₁ bent/quasi-linear Renner-Teller system ro-vibronic energy levels have been obtained from a variational approach accounting for anharmonicity, rotation-vibration and electronic angular momenta coupling effects. The vibronic levels are given for energies up to 13 500 cm^–1 for the bending levels and up to 8000 cm^–1 for the stretching and combination levels.Dedicated in the honor of Prof. Werner Kutzelnigg     

Systematic trends in the line strengths of E1 transitions in the carbon isoelectronic sequence

Line strengthsS for the dipole allowed transitions within then=2 complex of the carbon isoelectronic sequence have been fitted in the formZ ² S=A+B/(Z–C), whereZ is the nuclear charge of a particular ion. The constantsA,B andC are determined by using a non-linear least square method. The data forS is taken from the configuration interaction calculations which included internal, semi-internal and all external type correlations for ions in the rangeZ=8–26. It is shown that the values ofA obtained from the fit for all the transitions are in excellent accord with the ab-initio values obtained in the hydrogenic limitZ provided near degeneracy effects are included.