Marek Pawlikowski

Vibronic coupling effects in magnetic vibrational circular dichroism. A model formalism for doubly degenerate states

A formalism for magnetic vibrational circular dichroism (MVCD) of a model system is developed by considering vibronic coupling effects between a nondegenerate ground state and a degenerate excited state. Only one degenerate vibrational coordinate and one degenerate electronic excited state are considered in the model. A diabatic basis set representation was used for the vibronic functions paralleling previous Jahn–Teller effect formalisms. The parametrized model which results is shown to give MVCD A and B terms of a magnitude comparable to those previously observed for substituted benzenes. These model studies are suggestive that vibronic coupling effects are important for complete interpretation of MVCD spectra.

Vibronic Effects in the 11Bu(11B2) Excited Singlet States of Oligothiophenes. Fluorescence Study of the 11Ag(11A1) ← 11Bu(11B2) Transition in Terms of DFT, TDDFT, and CASSCF Methods

A combined DFT/TDDFT approach has been applied for calculating the Huang-Rhys (HR) parameters along the totally symmetric normal coordinates for the 1(1)A(g)(1(1)A(1)) <--1(1)B(u) (1(1)B(2)) electronic transition in a series of oligothiophenes containing from 2 to 6 thiophene rings. The calculations required optimized molecular geometries for both the ground state and the excited molecular state. The excited state geometry optimization was carried out by means of the time-dependent density functional theory (TDDFT) based methodology implemented in the Turbomole 5.9 (1) package of programs. The results for the three smallest oligothiophenes were verified by generating the theoretical vibronic structures and comparing them with the high-resolution fluorescence spectra measured for matrix-isolated molecules. For bithiophene a comparison was also made of the theoretical results obtained for different basis sets and the most popular exchange-correlation functionals. The best results were then confronted with the HR parameters based on the molecular geometries calculated at the CASSCF level of theory. The results obtained within the DFT/TDDFT approach are in very good agreement with the available experimental data for bithiophene, terthiophene, and quaterthiophene molecules.

Interference between intra- and inter-manifold couplings in resonance Raman spectra of metalloporphyrins☆

Abstract Anomalous intensity ratios in the excitation profiles of vibronically active fundamentals in the Q-band of porphyrins are shown to be due to interference between intramanifold (Jahn-Teller) coupling with the Q and B bands, intermanifold (Herzberg-Teller) coupling between the Q and B bands, and electronic configuration interaction between the one-electron representations of the corresponding excited states.

Resonance Raman study of Franck-Condon effects in the C10H8+ radical. Ab initio MCSCF calculations for the low-energy 2B2g and 2B3g symmetry states

Abstract Resonance Raman spectra in the region corresponding to the 2 A u ( D o ) → 1 2 B 3 g ( D 2 ) electronic excitation of the naphthalene cation (C 10 H 8 + ) are studied in terms of a model based on Franck-Condon (FC) effects. This simple model correctly accounts for the RRS spectra and yields FC parameters which correspond to those obtained from ab initio MCSCF computations. Computed FC activities of nine totally symmetric modes in the 2 B 3g (D 2 ) and 2 B 2g (D 4 ) states of the C 10 H 8 + radical are discussed and compared to experiment and earlier theoretical based studies on the ROHF/3-21G approach.

Absorption and circular dichroism spectra of dimeric systems. Extended dimer model

An extended dimer model is formulated. It differs from the simple dimer model in allowing for mixing of monomer electronic states by intermolecular interaction. The exact and approximate mathematical treatments of the model are discussed in detail. The model is applied to studies of absorption and circular dichroism spectra of dimers. It is shown that the transfer of intensity and rotatory power due to interstate mixing leads to readily observable changes in the vibronic structure of the corresponding spectra. The model is used to reinterpret the observed CD spectra of two different 1,1′‐bianthryls.

Franck–Condon effects in low-energy states of C10H8+ radical.: Ab initio MCSCF study of absorption and resonance Raman spectra

Abstract The Franck–Condon (FC) effects in the low-energy states of the C10H8+ radical are investigated in terms of ab initio FORS (full optimized reaction space) and SDE (single and double excitations) MCSCF calculational scheme applied with Dunnings double-zeta (DZV) basis set. This scheme is used to determine the excitation energies, the transition dipole moments and displacement (Franck–Condon) parameters for the three low-energy dipole-allowed 1 2 A u (D0)→ 1 2 B 3 g (D2), 1 2 A u (D0)→ 1 2 B 1 g (D3) and 1 2 A u (D0)→ 2 2 B 1 g (D4) transitions. The results of FORS MCSCF computations are compared to the QCFF/PI+CI and ROHF/3-21G results reported most recently for the C10H8+ radical. The resonance Raman (RR) spectra available in the region corresponding to the lowest-energy dipole-allowed 1 2 A u (D0)→ 1 2 B 3 g (D2) transition are discussed in some detail in the non-empirical fashion.

Resonance raman scattering in the region of a forbidden non-degenarate electronic state by a doubly degenerate vibration

Abstract It is shown that the resonance Raman scattering from a forbidden non-degenerate electronic state by a doubly degenerate mode depends strongly on Jahn—Teller interactions within an allowed doubly degenerate electronic state that lends its intensity to the scattering forbidden state.

The Franck–Condon effect in the lowest energy state of tetracyanoquinodimethane anion. The resonance Raman studies in terms of density functional theory

Abstract The absorption and resonance Raman (RR) excitation profiles (EPs) of ν 2 =2192 cm −1 , ν 4 =1389 cm −1 , ν 5 =1195 cm −1 and ν 9 =336 cm −1 fundamentals in the excitation region corresponding to 1 2 B 1g →1 2 B 2u transition in the tetracyanoquinodimethane (TCNQ) anion are studied in terms of vibronic model based on the Franck–Condon (FC) effect. The studies are carried out in terms of the local spin density Vosco–Wilk–Nusair (VWN) and the nonlocal spin density Becke–Perdew (BP) density functional theory (DFT) scheme applied with the double numerical functions augmented by polarization functions (DNP). The BP/DNP method leads to FC parameters, which only roughly correspond to those required to reconstruct the absorption and RR spectra. On the other hand, the VWN method is shown to offer reasonable, even if approximate, scheme to study the RR spectra of the TCNQ anion under resonance with the 1 2 B 1g →1 2 B 2u transition.

Multimode effects in resonance raman excitation profiles: 392 cm−1 fundamental of copper tetraphenyloporphyrin

Abstract It is shown that the resonance Raman excitation profile of the 392 cm −1 a 1g fundamental of copper tetraphenyloporphyrin observed in the region of the Q state can be explained by a strong mixing of this low-frequency mode with modes of high frequency (in the range of 1200–1600 cm −1 ) that are much more strongly vibronically active.

The electronic and vibrational structures of the vis–UV transitions in the 1,3-dicyanomethylene croconate anion in terms of CASSCF and DFT theory. The Franck–Condon analysis of 12B1→12A2 and 12B1→22A2 transitions

Abstract The visible and near UV absorption spectra of the 1,3-dicyanomethylene croconate anion radical are discussed in terms of density functional theory (DFT) and the complete active space (CASSCF) method employed with augmented cc-pVDZ basis set. It is shown that the three transitions 1 2 B 1 →2 2 A 2 , 1 2 B 1 →2 2 B 1 and 1 2 B 1 →3 2 B 1 shape the absorption in the near UV region. The FC activity in the most intense 1 2 B 1 →2 2 A 2 near UV transition was shown to be quite modest. On the other hand the near visible absorption of the croconate derivative is shown to be due to 1 2 B 1 →1 2 A 2 transition accompanied by a short progression of v5(a1)=1567 cm−1 mode.