Vibrational Coupling Constants Research Articles

Demonstration of resonant inelastic x-ray scattering as a probe of exciton-phonon coupling

Resonant inelastic X-ray scattering (RIXS) is a promising technique for obtaining electron-phonon coupling constants. However, the ability to extract these coupling constants throughout the Brillouin zone for crystalline materials remains limited. To address this need, we developed a Green's function formalism to capture electron-phonon contributions to core-level spectroscopies without explicitly solving the full vibronic problem. Our approach is based on the cumulant expansion of the Green's function combined with many-body theory calculated vibrational coupling constants. The methodology is applied to X-ray photoemission spectroscopy, X-ray absorption spectroscopy (XAS), and RIXS. In the case of the XAS and RIXS, we use a 2-particle exciton Green's function, which accounts implicitly for particle-hole interference effects that have previously proved difficult. To demonstrate the methodology and gain a deeper understanding of the experimental technique, we apply our formalism to small molecules, for which unambiguous experimental data exist. This comparison reveals that the vibronic coupling constant probed by RIXS is in fact related to exciton-phonon coupling rather than electron-phonon coupling, challenging the conventional interpretation of the experiment.

Infrared spectroscopy of 2ν4 and ν3 + 2ν4 bands of the NO3 radical

The 2ν4 band spectrum of 14NO3 observed with infrared diode laser spectroscopy was analyzed with the Fourier transform (FT) spectrum in the 760cm−1 region, including the Coriolis interaction between v4=2 and v2=1. The vibrational frequencies of v4=2, l=0, and l=±2 have been determined to be 752.4033(86) and 771.7941(81)cm−1, respectively. By considering the anharmonic interaction among the 2ν4, ν3, ν4, ν2, and ν2+3ν4 states, a relation among the cubic anharmonic constants was obtained as 0.452 Φ444ζ2,4−0.271 Φ344ζ2,3=127.7cm−1. The ratio of transition moments μ(ν2)/μ(2ν4) was determined to be 0.3 from the perturbation analysis. The second strongest infrared band of 14NO3, ν3+2ν4, observed around 1927cm−1has been analyzed with the hot band ν3+2ν4−ν4 by including the Coriolis interaction with the v2=1, v4=3 state. Similarly, the same band of 15NO3 was analyzed to give the band origin of 1897.9325(6)cm−1. The isotope shift 28.2cm−1 for the ν3+2ν4 vibrational frequency is consistent with a predicted value of 27.3cm−1. Although there are two A′ states in v3=1, v4=2, only one A2′ state has been assigned in the hot band, indicating that the other band has weak intensity. This fact and the strong intensity of the ν3+2ν4 band (l3=±1, l4=0) are understood as the effect of vibronic interaction. The first-order Coriolis coupling constant ζ of ν3+2ν4, l3=1, l4=0 is similar to those of the ν4 and ν3+ν4 states, and it is concluded that the vibrational Coriolis coupling constant is nearly zero and the observed constants of ζ=−0.19 (14NO3) and ζ=−0.15 (15NO3) also originate from the effect of vibronic interaction.

Effective representation of amide III, II, I, and A modes on local vibrational modes: Analysis of ab initio quantum calculation results

The Hamiltonian matrix for the first excited vibrational states of a protein can be effectively represented by local vibrational modes constituting amide III, II, I, and A modes to simulate various vibrational spectra. Methods for obtaining the Hamiltonian matrix from ab initio quantum calculation results are discussed, where the methods consist of three steps: selection of local vibrational mode coordinates, calculation of a reduced Hessian matrix, and extraction of the Hamiltonian matrix from the Hessian matrix. We introduce several methods for each step. The methods were assessed based on the density functional theory calculation results of 24 oligopeptides with four different peptide lengths and six different secondary structures. The completeness of a Hamiltonian matrix represented in the reduced local mode space is improved by adopting a specific atom group for each amide mode and reducing the effect of ignored local modes. The calculation results are also compared to previous models using C=O stretching vibration and transition dipole couplings. We found that local electric transition dipole moments of the amide modes are mainly bound on the local peptide planes. Their direction and magnitude are well conserved except amide A modes, which show large variation. Contrary to amide I modes, the vibrational coupling constants of amide III, II, and A modes obtained by analysis of a dipeptide are not transferable to oligopeptides with the same secondary conformation because coupling constants are affected by the surrounding atomic environment.

First analysis of the 2ν1 + 3ν3 band of NO2 at 7192.159 cm−1

The first investigation of the very weak 2ν1+3ν3 absorption band of nitrogen dioxide, 14N16O2, located at 7192.1587(1) cm−1 was performed using Fourier-transform incoherent broadband cavity-enhanced absorption spectroscopy (FT-IBBCEAS) in the 7080–7210cm−1 spectral range. The assigned 2ν1+3ν3 lines involve energy levels of the (203) vibrational state with rotational quantum numbers up to Ka=7 and N=47. Furthermore, due to local resonances involving energy levels from the (2,2,2)⇔(2,0,3) and (5,1,0)⇔(2,0,3) states, several transitions were also observed for the 2ν1+2ν2+2ν3 and 5ν1+ν3 dark bands, respectively. The energy levels were satisfactorily reproduced within their experimental uncertainty using a theoretical model which takes explicitly into account the Coriolis interactions between the levels of the (2,0,3) vibrational state and those of (2,2,2) and of (5,1,0). As a consequence, precise vibrational energies, rotational, and coupling constants were achieved for the triad {(5,0,1), (2,2,2), (2,0,3)} of interacting states of 14N16O2. This theoretical model also accounts for the electron spin-rotation resonances within the (2,0,3), (2,2,2) and (5,1,0) vibrational states. However, owing to the limited experimental resolution (∼0.075cm−1), it was not possible to observe the spin-rotation doublet structure. As a consequence, the spin-rotation constants in the {(2,2,2), (2,0,3), (5,1,0)} excited states were maintained fixed to their ground state values in this study. Using these parameters a comprehensive list of line positions and line intensities was generated for the 2ν1+3ν3 band of NO2.

Vibronic Coupling in the Ground State of Oligoacene Cations: The Performance of Range-Separated Hybrid Density Functionals

Oligoacenes such as naphthalene, anthracene, tetracene, and pentacene are among the best hole-transport organic semiconductors. An important parameter in the determination of the hole mobility is the coupling between the charge carrier and the vibrational modes. Here, we have evaluated the hole–vibration coupling constants in the radical-cation ground state of these molecules by means of the range-separated LC-ωPBE and ωB97 density functionals, with non-empirical optimization of the range-separation parameter ω. Our results indicate that both ω-tuned functionals yield similar relaxation energies and coupling constants. A comparison of the simulated vibrational structures of the first ionization band to the gas-phase ultraviolet photoelectron spectroscopy data underlines that the hole–vibration coupling constants derived by means of the non-empirically tuned LC-ωPBE and ωB97 functionals are in excellent agreement with experiment and superior to those derived from B3LYP calculations.

Influence of vibrations on electron transport through nanoscale contacts

In this paper, we present a novel semi‐analytical approach to calculate first‐order electron–vibration (EV) coupling constants within the framework of density functional theory. It combines analytical expressions for the first‐order derivative of the Kohn–Sham operator with respect to nuclear displacements with coupled‐perturbed Kohn–Sham theory to determine the derivative of the electronic density matrix. This allows us to efficiently compute accurate EV coupling constants.We apply our approach to describe inelastic electron tunneling (IET) spectra of metallic and molecular junctions. A gold junction bridged by an atomic chain is used to validate the developed method, reproducing established experimental and theoretical results. For octanedithiol and octanediamine single‐molecule junctions, we discuss the influence of the anchoring group and mechanical stretching on the IET spectra.

Computational IR spectroscopy of water: OH stretch frequencies, transition dipoles, and intermolecular vibrational coupling constants

The Hessian matrix reconstruction method initially developed to extract the basis mode frequencies, vibrational coupling constants, and transition dipoles of the delocalized amide I, II, and III vibrations of polypeptides and proteins from quantum chemistry calculation results is used to obtain those properties of delocalized O-H stretch modes in liquid water. Considering the water symmetric and asymmetric O-H stretch modes as basis modes, we here develop theoretical models relating vibrational frequencies, transition dipoles, and coupling constants of basis modes to local water configuration and solvent electric potential. Molecular dynamics simulation was performed to generate an ensemble of water configurations that was in turn used to construct vibrational Hamiltonian matrices. Obtaining the eigenvalues and eigenvectors of the matrices and using the time-averaging approximation method, which was developed by the Skinner group, to calculating the vibrational spectra of coupled oscillator systems, we could numerically simulate the O-H stretch IR spectrum of liquid water. The asymmetric line shape and weak shoulder bands were quantitatively reproduced by the present computational procedure based on vibrational exciton model, where the polarization effects on basis mode transition dipoles and inter-mode coupling constants were found to be crucial in quantitatively simulating the vibrational spectra of hydrogen-bond networking liquid water.

Disorder and order in unfolded and disordered peptides and proteins: A view derived from tripeptide conformational analysis. II. Tripeptides with short side chains populating asx and β‐type like turn conformations

In the preceding paper, we found that ensembles of tripeptides with long or bulky chains can include up to 20% of various turns. Here, we determine the structural and thermodynamic characteristics of GxG peptides with short polar and/or ionizable central residues (D, N, C), whose conformational distributions exhibit higher than average percentage (>20%) of turn conformations. To probe the side-chain conformations of these peptides, we determined the (3)J(H(α),H(β)) coupling constants and derived the population of three rotamers with χ1 -angles of -60°, 180° and 60°, which were correlated with residue propensities by DFT-calculations. For protonated GDG, the rotamer distribution provides additional evidence for asx-turns. A comparison of vibrational spectra and NMR coupling constants of protonated GDG, ionized GDG, and the protonated aspartic acid dipeptide revealed that side chain protonation increases the pPII content at the expense of turn populations. The charged terminal groups, however, have negligible influence on the conformational properties of the central residue. Like protonated GDG, cationic GCG samples asx-turns to a significant extent. The temperature dependence of the UVCD spectra and (3)J(H(N)H(α)) constants suggest that the turn populations of GDG and GNG are practically temperature-independent, indicating enthalpic and entropic stabilization. The temperature-independent J-coupling and UVCD spectra of GNG require a three-state model. Our results indicate that short side chains with hydrogen bonding capability in GxG segments of proteins may serve as hinge regions for establishing compact structures of unfolded proteins and peptides.

Evidence of charge delocalization in Ce1−xFex2+(3+)O2−ynanocrystals(x=0, 0.06, 0.12)

We have measured Raman scattering spectra of pure and iron-doped Ce${}_{1\ensuremath{-}x}$Fe${}_{x}$${}^{2+(3+)}$O${}_{2\ensuremath{-}y}$ ($x=0$, 0.06, and 0.12) nanocrystals. According to the x-ray diffraction study, Fe doping produces contraction of the CeO${}_{2}$ unit cell, leading to the Raman mode hardening. Contrary to expectation, the ${F}_{2g}$ Raman mode exhibits softening and broadening by changing the valence state of Fe dopant, as a consequence of the electron-molecular vibration coupling. This finding supports the assumption that additional charge in highly oxygen-deficient pure and Fe-doped CeO${}_{2\ensuremath{-}y}$ samples are not only localized at Ce${}^{3+}$ ions but also delocalized onto Ce(Fe)-O(V${}_{O}$)-Ce(Fe) orbitals. Delocalization of electrons from Ce${}^{3+}$ ions causes insulator-to-metal transition in highly oxygen-deficient nanoceria. The far-infrared reflectivity spectrum of nanoceria shows metalliclike reflectivity, which in the low-frequency region is well fitted with the Hagen-Rubens approximation for metals. Photoluminescence measurements revealed the existence of a defect-related band in the energy gap of CeO${}_{2\ensuremath{-}y}$. The electron-molecular vibration (phonon) coupling constants $\ensuremath{\lambda}$ and density of electron states at the Fermi level per spin and molecule $N(0)$ were determined within the framework of Allen's theory. The proposal of an energy band structure of nanoceria is also presented.

Formation of 2-imino-malononitrile and diaminomaleonitrile in nitrile rich environments: A quantum chemical study

Nitriles and nitrile chemistry are found in a variety of astronomical environments and have been utilized in many areas of astronomy and planetary science. Cyanogen (NCCN) has been observed in Titan’s atmosphere though it is not detected in comets or interstellar space. Nitriles formed in the atmosphere of Titan are expected to precipitate down onto the satellite’s surface where cosmic radiations can convert them into other molecules. In view of the significance of the HCN tetramers diaminomaleonitrile (DAMN) and diaminofumaronitrile (DAFN) in reactions leading to the formation of adenine, the possibility of their formation from CN and H radicals, which are known to be abundant in the nitrile rich astronomical environments, has been explored on the basis of radical–radical and radical–molecule interaction schemes using quantum chemical methods. Global and local descriptors such as chemical potential, molecular hardness and softness, electrophilicity and condensed Fukui functions were used to understand the mechanistic aspects of chemical reaction and region-selectivity of the CN and H radical additions. The presence and nature of weak bonds in the reaction complexes and transition states formed during the reaction process have been ascertained using Bader’s quantum theory of atoms in molecules (QTAIM). The reaction leading to the formation of DAFN is found to be exothermic with a very large net energy gain but involves a potential barrier of about 4.75kcal/mol. The present reaction scheme shall provide a simpler route to the formation of 4-amino-1H-imidazole-5-carbonitrile (AICN) and adenine. This reaction involves the formation of a neutral intermediate 2-imino-malononitrile for which no structural or spectroscopic information is available. A full vibrational analysis has, therefore, been attempted for 2-imino-malononitrile in the harmonic and anharmonic approximations and spectroscopic parameters such as rotational constants, rotation–vibration coupling constants, and centrifugal distortion constants are being reported.

Conformational and vibrational studies of isomeric hydrogen cyanide tetramers by quantum chemical methods

The results of structural studies and detailed harmonic and anharmonic vibrational analysis on two hydrogen cyanide (HCN) tetramers diaminomaleonitrile (DAMN) and diaminofumaronitrile (DAFN), which are important molecules for understanding the chemistry of interstellar space and nitrile rich environments, are being reported on the basis of density functional theory using second-order perturbation theory. Both the molecules are found to have C1 symmetry. While all the heavy atoms of DAMN lie in the same plane (maximum deviation 6°), the two nitrogen atoms in DAFN are out of plane by about 15°. The two amino groups are tetrahedral and do not have significant bond angle anisotropy. Detailed conformational studies are reported on the two molecules and their possible rotational isomers are identified. Complete vibrational analysis based on harmonic and anharmonic frequencies, intensity of infrared and activity of Raman bands and potential energy distribution over the internal coordinates has been provided for the two molecules. Affect of hydrogen bonding on molecular geometry and frequencies of the NH stretch modes has been studied by calculations on the dimers of the two molecules. A close agreement has been observed between the experimental and calculated frequencies. Vibrational–rotational constants such as rotational constants in the ground vibrational state (A0, B0, C0) and the effective rotational constants (Ae, Be and Ce), including terms due to quartic centrifugal distortion constants, rotation–vibration coupling constants, Wilson and Nielsen's centrifugal distortion constants have been calculated using B3LYP and B97-1 functionals and 6-31G**, 6-311+G** and TZVP basis sets.

Raman spectroscopic and low-temperature calorimetric investigation of the low-energy vibrational dynamics of hen egg-white lysozyme

The low-frequency vibrational dynamics of chicken hen egg-white lysozyme were investigated using Raman spectroscopy and low-temperature calorimetry. An amorphous-like behaviour of low-frequency dynamics was observed in this protein. By using inelastic light scattering data and resorting to a fitting procedure, the low-temperature specific heat trend was theoretically reproduced, confirming that, as in disordered systems, the same low-energy excitations give rise to the observed anomalies in low-frequency vibrational and low-temperature thermal properties. A further study of polarised and depolarised Raman spectra has allowed us to infer information about the symmetry of these modes. The frequency dependence of the light–vibrational coupling constant has also been analysed.

The (CH2)2O−H2O Hydrogen Bonded Complex. Ab Initio Calculations and Fourier Transform Infrared Spectroscopy from Neon Matrix and a New Supersonic Jet Experiment Coupled to the Infrared AILES Beamline of Synchrotron SOLEIL

A series of hydrogen bonded complexes involving oxirane and water molecules have been studied. In this paper we report on the vibrational study of the oxirane-water complex (CH(2))(2)O-H(2)O. Neon matrix experiments and ab initio anharmonic vibrational calculations have been performed, providing a consistent set of vibrational frequencies and anharmonic coupling constants. The implementation of a new large flow supersonic jet coupled to the Bruker IFS 125 HR spectrometer at the infrared AILES beamline of the French synchrotron SOLEIL (Jet-AILES) enabled us to record first jet-cooled Fourier transform infrared spectra of oxirane-water complexes at different resolutions down to 0.2 cm(-1). Rovibrational parameters and a lower bound of the predissociation lifetime of 25 ps for the v(OH)(b) = 1 state have been derived from the rovibrational analysis of the ν(OH)(b) band contour recorded at respective rotational temperatures of 12 K (Jet-AILES) and 35 K (LADIR jet).

Axial and equatorial hydrogen-bond conformers between (CH2)3S and H(D)F: Fourier transform infrared spectroscopy and ab initio calculations

The coexistence of axial and equatorial hydrogen-bonded conformers of 1 : 1 (CH(2))(3)S-HF (and -DF) has been observed in the same adiabatic expansion of a supersonic jet seeded with argon and in a static absorption cell at room temperature. High level calculations computed the axial conformer to be the most stable one with a small energy difference with respect to the equatorial one, in full agreement with previous microwave experiments. On the grounds of band contour simulations of FTIR spectra and ab initio energetic and anharmonic vibrational calculations, two pairs of ν(s) HF donor stretching bands, observed in a series of jet-FTIR spectra at 3457.9 and 3480.5 cm(-1) have been respectively assigned to the axial and equatorial forms of the 1 : 1 complex. In the jet-FTIR spectra series with HF, the assignment of an additional broad band (about 200 cm(-1) higher in frequency with respect to ν(s)) to a 1 : 2 complex has been supported by theoretical investigations. Experimental detection of both axial and equatorial forms of a cyclic trimer has been confirmed by calculated energetic and vibrational properties. The nature of hydrogen bonding has been examined within topological frameworks. The energetic partitioning within the 1 : 1 dimers has been elucidated with SAPT techniques. Interestingly, the interconversion pathway between two 1 : 1 structures has been explored and it was seen that the formation of the 1 : 1 complex affects the interconversion barrier on the ring puckering motion. The band contour analysis of gas phase FTIR experiments provided a consistent set of vibrational frequencies and anharmonic coupling constants, in good agreement with ab initio anharmonic vibrational calculations. Finally, from a series of cell-FTIR spectra recorded at different partial pressures of (CH(2))(3)S and HF monomers, the absorption signal of the 1 : 1 complex could be isolated which enabled to estimate the equilibrium constant K(p) = 0.023 at 298 K for the dimerization.

Analysis of the absorption spectra and spectral hole burning in zero-phonon lines of F+3 and N1 colour centres in LiF crystals

The temperature dependences and mechanisms of broadening of zero-phonon lines of F+3 (488 nm) and N1 (523 nm) colour centres in LiF crystals are investigated. The results obtained make it possible to determine the quadratic electronic—vibrational coupling constant for N1 colour centres. The experimental data on the spectral hole burning in zero-phonon lines of F+3 and N1 colour centres indicate that the latter are positively charged.

First high-resolution analysis of the 4ν 1+ν 3 band of nitrogen dioxide near 1.5 μm

The high-resolution absorption spectrum of the 4ν 1+ν 3 band of the 14N 16O 2 molecule was recorded by CW-Cavity Ring Down Spectroscopy between 6575 and 6700 cm −1. The assignments involve energy levels of the (4,0,1) vibrational state with rotational quantum numbers up to K a=8 and N=48. A large majority of the spin-rotation energy levels were reproduced within their experimental uncertainty using a theoretical model which takes explicitly into account the Coriolis interactions between the spin-rotational levels of the (4,0,1) vibrational state and those of the (4,2,0) and of (0,9,0) dark states, the anharmonic interactions between the (4,2,0) and (0,9,0) states together with the electron spin-rotation resonances within the (4,0,1), (4,2,0) and (0,9,0) states. Precise vibrational energies, rotational, spin-rotational, and coupling constants were determined for the {(4,2,0), (0,9,0), (4,0,1)} triad of interacting states. Using these parameters and the value of the transition dipole-moment operator determined from a fit of a selection of experimental line intensities, the synthetic spectrum of the 4ν 1+ν 3 band was generated and is provided as Supplementary Material.

The role of cluster energy nonaccommodation in atmospheric sulfuric acid nucleation

We discuss the possible role of energy nonaccommodation (monomer-cluster collisions that do not result in stable product formation due to liberated excess energy) in atmospheric nucleation processes involving sulfuric acid. Qualitative estimates of the role of nonaccommodation are computed using quantum Rice-Ramsberger-Kassel theory together with quantum chemically calculated vibrational frequencies and anharmonic coupling constants for small sulfuric acid-containing clusters. We find that energy nonaccommodation effects may, at most, decrease the net formation rate of sulfuric acid dimers by up to a factor of 10 with respect to the hard-sphere collision rate. A decrease in energy nonaccommodation due to an increasing number of internal degrees of freedom may kinetically slightly favor the participation of amines rather than ammonia as stabilizing agents in sulfuric acid nucleation, though the kinetic enhancement factor is likely to be less than three. However, hydration of the clusters (which always occurs in ambient conditions) is likely to increase the energy accommodation factor, reducing the role that energy nonaccommodation plays in atmospheric nucleation.

Experimental and Theoretical Spectroscopic Study of 310 Helical Peptides using Isotopic Labeling

Experimental and theoretical studies of IR, VCD, and Raman spectra have been performed on synthesized peptides (iPrCO-Aib-L-Ala-Aib-L-Ala-L-Ala-Aib-NHiPr) having a 310-helical conformation. These sequences vary only due to isotopic labeling (13C=O) of the L-Ala on the relative (i , i +1), (i, i + 2), and(i, i + 3) positions. Di-alkyl substitution on the α-carbon of Aib restricts the rotational freedom of the backbone torsional angles (f, ψ) and favors the formation of 310-helices [1]. Theoretical IR, VCD and Raman simulations were performed on sequences identical to the synthesized ones but constrained (in terms of f, ψ torsional angles) to an ideal 310-helical geometry (−60, −30) and fully optimizing all the other coordinates. All calculations were performed for peptides in vacuum using the DFT BPW91/6-31G∗ level of theory. The simulations predicated the relative separations of 13C=O and 12C=O features and their dependence on conformation as seen experimentally, with the exception that end effects caused a change in diagonal force field not well represented in the theoretical modeling. Experimental spectra for longer sequences and singly labeled variants confirmed the source of deviation for the i,i+1 and i,i+3 models. Comparison of IR and VCD intensity patters helped sort out the vibrational coupling constants sensed in the 13C=O modes. The isotopic labeled group vibrations are coupled to each other most strongly when degenerate and are effectively uncoupled from those of the unlabeled groups.[1] Wang et al., Peptide Science, 2009, 92, 452-456.

Electron-intramolecular vibration coupling in TTF-TCNQ systems

We report calculations of the linear electron molecular vibration coupling constants in TCNQ, TCNQ−, and TTF. A complete neglect of differential overlap (cndo) type parameterization is used for the electronic structure and a modified valence force field (mvff) approach for the determination of the vibrational normal modes. Direct experimental information on the magnitude of the coupling constants can be obtained in the gaseous phase from photoemission experiments and in the solid state from polarized optical reflectance measurements on organic linear chain conductors. Agreement between theory and experiment is good. The relevance of electron-intramolecular vibrational coupling constants for the stabilization of the charge density wave (cdw) state in TCNQ anion radical salts and in the determination of polaron binding energies is stressed.

Charge-transfer processes in radical ion molecular conductors κ-(BEDT-TTF)2Cu[N(CN)2]Br x Cl1 − x : The superconductor (x = 0.9) and the conductor with the metal-insulator transition (x = 0)

Optical spectral investigations of low-dimensional organic molecular conductors κ-(BEDT-TTF)2Cu[N(CN)2]Br x Cl1 − x with x = 0.9 (the superconductor with T c = 11.3 K) and x = 0 (the metal with the metal-insulator transition at T < 50 K) are performed in the range 50–6000 cm−1 (6 meV–0.74 eV) at temperatures from 300 to 20 K. The optical conductivity spectra are quantitatively analyzed in terms of the proposed model, according to which the charge transfer involves two types of charge carriers, i.e., electrons (holes) localized on clusters (dimers and tetramers formed by BEDT-TTF molecules) and quasi-free charge carriers, with the use of the tetramer “cluster“ model based on the Hubbard Hamiltonian for correlated electrons and the Drude model for quasi-free charge carriers. Physical parameters of the model, such as the energy of Coulomb repulsion between two electrons (holes) in one molecule, the transfer integrals between molecules inside the dimer and between dimers, and the electron-molecular vibration coupling constants, are determined. The anisotropy of the spectra in the conducting plane is explained. The inference is made that only electrons localized on clusters couple with intramolecular vibrations.