Vibrational structure of the electron transition to the second excited singlet state of pyridine N-oxide

The vibrational structure of the electron transition to the second singlet excited state of pyridine N-oxide has been studied. The frequency of the 0–0 transition is 34502 cm⁻¹. A computer-aided technique for the assignment of the frequencies of the normal vibrations of polyatomic molecules in the excited electronic states is proposed. The frequencies of the totally symmetric vibrations of pyridine N-oxide in the second singlet electronically excited state are assigned. N. G. Chernyshevskii Saratov State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 350–355, March–April, 1995. Translated by I. Izvekova     

Electronic absorption spectrum of pyridine N-oxide in the gas phase. General characterization

The full electronic absorption spectrum of pyridine N-oxide vapor in the near ultraviolet region has been obtained. The vibronic structure has been analyzed in detail. The four absorption bands, which are observed at 341, 290, 228, and 217 nm, correspond to four 0–0 vibronic transitions. The spectrum is interpreted in terms of the CNDO/S method. The symmetry of the vibrations that exhibit activity due to the Herzberg-Teller effect in different electronic states has been studied. N. G. Chernyshevskii Saratov State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 345–349, March–April, 1995. Translated by I. Izvekova     

S1←S0 vibronic spectrum and structure of fluoral in the S1 state

The vibronic absorption spectrum of fluoral vapor was studied in the region of the S₁←S₀ electronic transition (313–360 nm). The origin O₀ ⁰⁺) of the transition (29419 cm⁻¹) and a number of fundamental frequencies in the S₀ and S₁ states were determined. The character of intensity distribution in the spectral bands indicates that the electronic excitation leads to significant change of the CF₃ group orientation relative to the molecular frame. Moreover, it was found that the carbonyl fragment of the molecule in the S₁ state has pyramidal structure (in contrast, the carbonyl fragment of the fluoral molecule in the S₀ state is planar). The experimental torsion and inversion energy levels were used for the calculation of internal rotation and inversion potential functions of fluoral molecule in the S₁ state. The potential barriers to internal rotation and inversion were found to be 1270 cm⁻¹ (15.2 kJ mol⁻¹) and 550 cm⁻¹ (6.6 kJ mol⁻¹), respectively. The conformational changes caused by S₁←S₀ electronic excitation in the fluoral molecule are similar to those observed in acetaldehyde and biacetyl molecules and differ from the conformational behavior of hexafluorobiacetyl molecule. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 294–299, February, 1998.     

S 1 ←S 0 vibronic spectrum and the structure of the chloral molecule in theS 1 stateS 0 vibronic spectrum and the structure of the chloral molecule in theS 1 state

The vibronic absorption spectrum of chloral (CCl₃COH) vapors is studied in the region of S₁ ← S₀ electron transition (32,000–28,700 cm⁻¹). The 29,070 cm⁻¹ vibronic transition (not observed because of low intensity) is believed to be the ‘start’ of the electron transition. Several fundamentals are found in the S₀ and S₁ states. Inversion splitting of the zero vibrational level in the S₁ state of chloral, indicating a nonplanar structure of the carbonyl fragment, is found. The intensity ratio of the torsional transition bands indicates that the S₁ ← S₀ electronic excitation of the chloral molecule causes significant changes in the orientation of the −CCl₃ group relative to the molecular framework. The potential functions of internal rotation (S₀ and S₁ states) and inversion (S₁ state) of the chloral molecule are determined from experimental data. The potential barriers of internal rotation (S₀ and S₁ states) and inversion (S₁ state) are 380, 780, and 760 cm⁻¹ (4.5, 9.3, and 9.1 kJ/mole), respectively. M. V. Lomonosov Moscow State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 3, pp. 507–513, May–June, 1998.     

Vibronic coupling of pyrene in the first ππ* excited state

The two-photon fluorescence excitation spectrum of pyrene in n-hexane and n-heptane matrices has been measured at 10 K in the region of the first electronic transition (26800–30200 cm^?1). The spectrum consists of a rich number of sharp bands, being in general better resolved in n-hexane than in n-heptane matrix. Shpol'skii multiplets have been observed for the most intense bands. A strong two-photon band dominates the spectrum = 1495 cm^?1 from the 0—0 line and was assigned to B_1u × b_1u = A_g symmetry. Other weaker vibronic origins occur in the spectrum which were correlated to vibrational modes of b_1u, b_2u, b_3u and a_u symmetry. Intense vibronic bands are observed close to the origin of the second electronic transition and were interpreted as combination bands of B_1u × b_1u × b_3g symmetry. A two-photon vibronic theory to account for their intensity is proposed where the electronic moment is linearly expanded in powers of the nuclear displacements.     

Parametric method in the theory of the vibronic spectra of complex molecules. Absorption spectrum of decapentaene

The absorption spectra of decapentaene are analyzed and calculated using the available efficient methods of calculating the matric elements of the vibronic problem, a new parametric method for determining the potential surfaces of excited molecules, and a fragmentation approach to the design of molecular models. Good agreement for the fine vibrational structure of the calculated and experimental spectra (differences between the main band frequencies and intensities less than 20 cm⁻¹ and 10%, respectively) is obtained without correcting the parameters of the method. The mechanisms of excitation-induced structural changes in linear polyenes and the effect of bond angle changes on the vibrational structure of the spectrum are revealed. A new interpretation of the absorption spectrum of decapentaene in an argon matrix is proposed [J. Mol. Spectrosc.,114, 54–59 (1985)]. It is shown that the parametric method allows quantitative prediction of fine structure for the vibronic spectra of complex molecules. K. A. Timiryazev Moscow Agricultural Academy. Translated fromZhurnal Strukturmoi Khimii, Vol. 37, No. 6, pp. 1031–1039, November–December, 1996. Translated by I. Izvekova     

Photoinduced isomerization of 4-(4′-dimethylaminostyryl) pyridine N-oxide

The effects of photoirradiation on the conformation state of 4-(4′-dimethylaminostyryl)pyridine N-oxide was studied by spectral (EAS, ¹H NMR, IR) and thermochemical methods. Trans→cis isomerization was found to proceed in 4-(4′-dimethylaminostyryl)pyridine N-oxide irradiated with light (λ ≤ 400 nm) in chloroform. The conversion of the trans form of 4-(4′-dimethylaminostyryl)pyridine N-oxide to the cis form depends on the time and intensity of irradiation. Maximum conversion was achieved when a photostationary mixture formed with a ratio of components trans:cis = 40:60. Further irradiation of the solutions of 4-(4′-dimethylaminostyryl)pyridine N-oxide in chloroform led to salification with HCl formed during the decomposition of CHCl₃.     

Electronic structure, spectrum, and intramolecular electron transfer model of [(NH3)5Ru-(4,4’-bipy)-Ru(NH3)5]5+

The electronic structure of the ground and excited states of the binuclear mixed-valence complex [Ru(NH₃)₅]₂(4,4’-bipy)⁵⁺ is calculated by the semiempirical INDO + CI method, and an electronic spectrum assignment is given. A theoretical model of electron transfer between the Ru(II) and Ru(III) metal centers is constructed on the basis of many-electron wave functions. The dependence of the electron transfer characteristics on the angles between the planes of the pyridine rings and also between the pyridine rings and the planes of cis(NH₃)-Ru-cis(NH₃) is analyzed. Translated fromZhumal Struktumoi Khimii, Vol. 38, No. 3, pp. 447–456, May–June, 1997.     

Crystal structure and magnetic properties of the octahedral complexes of Ni(II) with 3-imidazoline nitroxides

This paper reports on our studies of the crystal structures and magnetic properties of five mixed-ligand octahedral complexes of Ni(II) with 3-imidazoline nitroxides Ni(RL)₂X₂, where RL are deprotonated enaminoketone derivatives of 3-imidazoline nitroxide with different substituents R (CF₃, Ph) in the side chain, and X is pyridine, dimethylsulfoxide, or semi-phenanthroline. It is established that this type of heterospin system is characterized by an intramolecular exchange interaction parameter (J) of an order of 10 cm⁻¹. Substitution of the N-donor diamagnetic pyridine or phenanthroline by the O-donor dimethylsulfoxide in the coordination sphere of the metal decreases J by 2–3 cm⁻³. A transition from trans-to cis-coordination of the enaminoketone ligands and variation of the R substituent in the chelate ring do not affect the value of J. Deceased. Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 5, pp. 901–916, September–October, 1998. This work was supported by INTAS grant No. 94-3508 and RFFR grants No. 96-03-33738 and 96-03-32229.     

The S1 ← S0 vibronic spectra and structure of the (CH3)2 CHCHO and (CH3)2 CHCDO 2-methylpropanal molecules

A multipass cell with an optical path up to 120 m long was used to measure the vibronic absorption spectra of 2-methylpropanal-h₁ (MPA-h₁, (CH₃)₂CHCHO)) and 2-methylpropanal-d₁ (MPA-d₁, (CH₃)₂CHCDO)) over the frequency range 28200–31600 cm⁻¹. The most intense spectral lines were assigned to transitions from vibrational levels of the cis and gauche MPA-h₁ and MPA-d₁ conformers in the ground electronic state (S ₀) to vibrational levels of conformers 1 and 3 in the lowest singlet excited electronic state (S ₁). According to our estimates, the origins (0 ₀ ⁰ ) of the 1 S ₁) ← cis(S ₀) and 3(S ₁) ← cis(S ₀) and also 1(S ₁) ← gauche(S ₀) and 3(S ₁) ← gauche(S ₀) electronic transitions were situated at 29147 and 29177, 29391 and 29417 cm⁻¹, respectively, for MPA-h₁ and at 29226 and 29240, 29480 and 29500 cm⁻¹ for MPA-d₁. The structure of conformers 1 and 3 in the S ₁ state was shown to differ from the structure of the cis and gauche conformers in the S ₀ state by the angle of rotation of the (CH₃)₂CH-isopropyl top and “pyramidal distortion” of the CCHO/CCDO carbonyl fragment. A series of fundamental frequencies of MPA conformers in different electronic states were found. The potential functions of inversion were determined for the conformer 1-conformer 3 pairs of MPA-h₁ and MPA-d₁ from the experimental energy levels of inversion vibrations. The potential barriers to inversion and equilibrium displacements of the CH/CD bond out of the CCO plane were found to be 735/675 cm⁻¹ and ±34°/±32° for MPA-h₁ and MPA-d₁, respectively. Original Russian Text ? I.A. Godunov, S.L. Lur’e, N.N. Yakovlev, V.A. Bataev, 2007, published in Zhurnal Fizicheskoi Khimii, 2007, Vol. 81, No. 1, pp. 52–62.     

S1←S0 Vibronic spectrum and structure of 2,2-difluoroethanal in the S1 state

The vibronic spectrum of the 2,2-difluoroethanal vapor was recorded using a multipass optical cell with an optical length of at least 140 m. The spectrum in the region of 300—364 nm was assigned to the S₁S₀ electronic transition (from the ground S₀ to the first excited singlet S₁ electronic state); the vibrational structure of the spectrum was analyzed. The spectrum bands were assigned to two systems of vibronic transitions, namely, transitions between the levels of the cis-conformer (S₀) and of the S₁ conformers, with the origins (0₀ ⁰ transitions between the zero vibrational levels of conformers) at 29192 and 29087 cm^–1, respectively. Analysis of the spectrum showed that the S₁S₀ electronic excitation of the cis-conformer was followed by rotation of the CHF₂ top and pyramidal distortion of the carbonyl fragment. A number of fundamental frequencies were found for S₁ conformers, in particular, torsion and inversion energy levels. The experimental data are in satisfactory agreement with the results of quantum-chemical calculations for the 2,2-difluoroethanal molecule in the S₀ and S₁ states.     

Selectivity of vibronic coupling in complex molecules with benzene fragments

This paper deals with the mechanisms of localization of Franck-Condon vibronic coupling of πσ^*- or πlπ^*-orbital type in a few vibrational modes, (LVM) in excited electronic states of polyatomic molecules. The analysis of vibronic coupling uses highly symmetric basis sets (for representing MO structures and normal coordinates ξ_R) as well as simplified models that relate the shift Δ_R of the electron potential minima along the normal coordinates to the MO structure and to ξ_R in the form of analytical expressions. The modes that are active in LVM are determined from the experimental luminescence spectra. These ideas about approximately high local symmetry of vibronic coupling in benzene fragments as well as the estimates of Δ_R depending on variations in the MO structure explain the experimental results. L. Ya. Karpov Physicochemical Scientific Research Institute. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 286–291, March–April, 1995. Translated by L. Smolina     

Simulation and interpretation of the vibrational spectra of heterofullerenes

This paper reports on a computer simulation of the vibrational spectra of C₅₉B, C₅₉N, C₅₉BN, and C₅₉HN. The modes whose frequencies are most sensitive to carbon substitution by heteroatoms are revealed. It is shown that the new bands at 818, 839, and 845 cm⁻¹ in the experimental IR spectrum of C₅₉HN arise from changes in selection rules and by removal of degeneracies due to a reduction in the symmetry of the molecule and force field perturbation. In the Raman spectrum of C₅₉HN, the shifts of the 1460 and 491 cm⁻¹ bands to the low-frequency region by 7 and 3 cm⁻¹, respectively, relative to two A_g modes of C₆₀ are explained by the perturbation induced by the N and C(H) atoms in the force field of adjacent CC bonds not containing these atoms. Institute of Spectroscopy, Russian Academy of Sciences (Troitsk, Moscow Region). Scientific and Production Association “Complex.” Scientific and Production Association “Tekhon.” Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 3, pp. 401–411, May–June, 1998.     

Reinterpretation of the fluorescence excitation spectrum of hexafluorobiacetyl in a supersonic jet

The results of the analysis of the fluorescence excitation spectrum of trans-hexafluorobiacetyl published earlier are revised. New values of torsion frequencies and potential barriers of internal rotation of the CF₃ group in the ground and excited states of the molecule are obtained. A procedure for calculating the probabilities of torsional vibronic transitions of molecules is described. Translated fromZhurnal Struktumoi Khirnii, Vol. 38, No. 2, pp. 293–302, March–April, 1997.     

Comparative analysis of the vibrational structure of the absorption spectra of acrolein in the excited (<Emphasis Type="Italic">S</Emphasis><Subscript>1</Subscript>) electronic state

The assignments of absorption bands of the vibrational structure of the UV spectrum are compared with the assignments of bands obtained by the CRDS method in a supersonic jet from the time of laser radiation damping for the trans isomer of acrolein in the excited (S ₁) electronic state. The ν_00trans = 25861 cm⁻¹ values and fundamental frequencies, including torsional vibration frequency, obtained by the two methods were found to coincide in the excited electronic state (S ₁) for this isomer. The assignments of several absorption bands of the vibrational structure of the spectrum obtained by the CRDS method were changed. Changes in the assignment of (0-v′) transition bands of the torsional vibration of the trans isomer in the Deslandres table from the ν_00trans trans origin allowed the table to be extended to high quantum numbers v′. The torsional vibration frequencies up to v′ = 5 were found to be close to the frequencies found by analyzing the vibrational structure of the UV spectrum and calculated quantum-mechanically. The coincidence of the barrier to internal rotation (the cis-trans transition) in the one-dimensional model with that calculated quantum-mechanically using the two-dimensional model corresponds to a planar structure of the acrolein molecule in the excited (S ₁) electronic state.     

Vibronic spectra of the allyl radical at 6–8 eV with resonance-enhanced multiphoton ionization technique

The allyl radical was produced in molecular beam by pyrolysis of allyl iodide. The vibronic spectra from ground state to six new electronic states of the allyl radical at 6–8 eV, π →3d^xz, π →3d^xy and π →ns (n=4, 6, 7, 8) were observed firstly with the aid of time-of-flight mass spectros copy and resonance-enhanced multiphoton ionization technique. Vibrational progression ofv ₇(C₃ bend) with gross spacing of about 430 cm⁻¹ was observed inns Rydberg states. The adiabatic ionization potential of the allyl radical was obtained to be (65641 ± 20) cm⁻¹ ((8.138 ± 0.002) eV) by fitting the term values ofns (n=4,6,7,8) Rydberg states with Rydberg formula.     

Infrared and Raman spectra and thermodynamic functions of 4-methoxypyridine N-oxide

The infrared spectrum of 4-methoxypyridine N-oxide in the region 4000-30 cm⁻¹ in the solid and liquid states and the polarized laser Raman spectrum of the molecule in the liquid state have been investigated. A vibrational assignment of the observed frequencies based on the state of polarization of the Raman lines and comparison with the related molecules is presented. Ideal gas state thermodynamic functions of the molecule are calculated in the temperature range 273·15–1500° K.     

EPR spectroscopy of quintet 4-amino-3,5-dichloropyridine-2,6-diyldinitrene isolated in solid argon

An EPR spectrum of solid Ar isolated quintet 4-amino-3,5-dichloropyridin-2,6-diyldinitrene that formed by the photolysis of 4-amino-2,6-diazido-3,5-dichloropyridine at 15 K was recorded. Using computer simulation based on numerical diagonalization of the quintet spin Hamiltonian matrices, it was established that this EPR spectrum corresponds to a quintet spin state with the magnetic parameters g = 2.0023, |D _q| = 0.2100 cm⁻¹, and |E _q| = 0.0560 cm⁻¹. Owing to high resolution of the experimental spectrum, the zero-field splitting parameters of the quintet intermediate were determined to an accuracy of at least 5·10⁻⁴ cm⁻¹. Calculations of the fine-structure energy levels in external magnetic field and the dependences of the EPR signal positions and intensities of the quintet dinitrene on the direction of external magnetic field were performed for the first time. This allowed unambiguous assignment of all EPR lines of quintet molecules having both in-principal-axis and off-principal-axis orientations. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2284–2289, December, 2007.     

Specific spectral properties of a photochromic ferromagnetic (C25H23N3O3Cl)CrMn(C2O4)3·H2O

A molecular magnetic (C₂₅H₂₃N₃O₃Cl)CrMn(C₂O₄)₃·H₂O whose spiropyran cation contains a quaternized pyridine fragment in the side aliphatic chain was synthesized for the first time. The compound possesses the properties of a ferromagnetic with T _c = 5.2 K and photochromic properties in the crystalline state. The photochemical properties of the hybrid compound were studied by electronic and IR spectroscopies. Photochromic transformations of the spiropyran cation are accompanied by the appearance of a broad absorption band in the region 400–600 nm in the electronic spectra and by reduction of intensity of the ν(C_spiro-O) IR band at 942 cm⁻¹. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1055–1061, June, 2007.     

Synthesis, spectral and electrochemical study of coordination molecules Cu4OX6L4: 3-cyanopyridine Cu4OBrnCl(6?n)(3-CNpy)4 complexes

New 4-cyanopyridine halide and mixed-halide Cu₄OBr _n Cl_(6−n)(4-CNpy)₄ complexes (4-CNpy = 4-cyanopyridine, n = 0–6) were synthesised, characterised, and studied by infrared spectra, electronic spectra, and cyclic voltammetry. Infrared spectra revealed donor-acceptor vibrational couplings of the Cu₄O, Cu-Cl, and Cu-N stretching vibrations with the in-plane and out-of-plane pyridine ring vibrations. The infrared spectra, electronic spectra, and half-wave potentials correspond to a weak donor and a strong acceptor behaviour of the 4-cyanopyridine ligands and to π-back bonding, Cu(II)→pyridine rings. The results were compared with the related pyridine and 4-substituted pyridine complexes.