High-level studies of the singlet states of quadricyclane, including analysis of a new experimental vacuum ultraviolet absorption spectrum by configuration interaction and density functional calculations (original) (raw)
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The Journal of Chemical Physics
The vacuum ultraviolet spectrum (VUV) for cyclohepta-1,3,5-triene (CHT) up to 10.8 eV shows several broad bands, which are compared with electron impact spectra. Local curve fitting exposed groups of sharp vibrational peaks, which are assigned to Rydberg states. The vertical excitation profile of the VUV spectrum, reproduced by time dependent density functional theory (TDDFT), gives a good interpretation of the principal regions of absorption. Fourth order Möller-Plessett perturbation theory, including single, double and quadruple excitations (MP4(SDQ)), showed that the lowest singlet and triplet states retain CS symmetry. This contrasts with TDDFT where several low-lying excited states are planar. Detailed vibrational analysis of the first UV band was performed by Franck-Condon (FC), Herzberg-Teller (HT), and their combined methods (FCHT). These show the dominance of mid-range
The Journal of Chemical Physics
A new synchrotron-based study of the vacuum ultraviolet (VUV) absorption spectrum for cyclooctatetraene (COT) shows a series of broad peaks. A significant sharp structure was extracted from the strongest band between 5.9 and 6.3 eV by fitting this range of the spectrum to a polynomial; the regular residuals show a set of sharp peaks. Comparison of this region of the VUV with the photoelectron spectrum demonstrates the presence of several Rydberg states, all based on the lowest observed ionization energy ionic state. The UV onset contains a broad band in the range 4.0 eV-5.3 eV. Theoretical vertical excitation energies, determined by configuration interaction (CI) studies at the multireference multiroot singles and doubles CI level, enabled interpretation of the principal absorption bands of the VUV spectrum. Adiabatic excitation energies (AEEs) for several singlet and triplet valence states (V) were evaluated by multiconfiguration self-consistent field methods. Theoretical Rydberg series AEEs were obtained by use of extremely diffuse Gaussian orbitals in highly correlated wave-functions. The second moments of the charge distribution identify which roots are valence or Rydberg states. A contrast was found between some density functional methods and Hartree-Fock (HF) wave-functions during single-excitation CI, when degenerate orbitals were involved in the leading configurations. The 7a 1 6e * state contained the expected 8-membered ring in the density functional theory calculations. The HF wave-functions led to a 1,5-cross-ring interaction which converged on a singlet excited state of a bicyclo[3,3,0]octatriene; this is reminiscent of the photochemical conversion of COT to semibullvalene.
2021
A synchrotron-based vacuum ultraviolet (VUV) absorption spectrum of norbornadiene (NBD) is reported, and the extensive vibrational structure obtained has been analyzed. The previously known 5b13s-Rydberg state has been reinterpreted by comparison with our recent high-resolution photoelectron spectral analysis of the X2B1 ionic state. Additional vibrational details in the region of this Rydberg state are observed in its VUV spectrum when compared with the photoelectron 2B1 ionic state; this is attributed to the underlying valence state structure in the VUV. Valence and Rydberg state energies have been obtained by configuration interaction and time-dependent density functional theoretical methods. Several low-lying singlet valence states, especially those that arise from ππ* excitations, conventionally termed NV1 to NV4, have been examined in detail. Their Franck-Condon (FC) and Herzberg-Teller (HT) profiles have been investigated and fitted to the VUV spectrum. Estimates of the exper...
Chemical Physics Letters, 2007
Franck-Condon simulations of the vibronic spectra of the styrene S 1 and S 2 states, based on geometries and force fields obtained with Time Dependent Density Functional Theory, are reported. Excellent agreement is obtained with experimentally observed vibrationally resolved excitation and emission spectra, allowing us to verify previous assignments and interpretations and, ultimately, to determine the changes in geometry and force field upon excitation. The influence of the choice of the exchange correlation functional on the calculated excitation energy, molecular geometry, and oscillator strength has been investigated and found to be less critical than what was conjectured from previous studies.
The Journal of Chemical Physics, 1994
Laser-induced fluorescence spectra of the 36 K6 and 36 K6 vibronic bands of the A lAu+-X l~: transition in acetylene have been recorded with a resolution of 18 MHz. Each rotational transition consists of a group of lines due to coupling of the electronically excited singlet state with isoenergetic triplet states. Using the standard deconvolution procedure the singlet-triplet coupling elements and the density of coupled triplet states are derived for rotational le~els up to J = 4 in both bands. From the density of coupled triplet states it is concluded that the AlA u state is perturbed by the Tl 3 B2 state. Magnetic field me~surements have shown that the predissociation of acetylene in the 4vi vibrational level of the A state is caused by a coupling via the T 1 3 B2 state with predissociating vibrational levels of the electronic ground state.
Journal of the American Chemical Society, 1997
The lowest excited singlet states of the structurally rigid amines 1-azaadamantane and 1-azabicyclo[2.2.2]octane have been investigated by using fluorescence excitation spectroscopy on samples seeded in supersonic expansions. Based upon the notion that in both species the lowest excited singlet state is a Rydberg state with the ground state of the radical cation as its ionic core, excitation spectra have been analyzed by employing density functional calculations of the equilibrium geometries and force fields of the ground state of the neutral species and its radical cation. A good agreement is obtained between experimentally observed and theoretically predicted frequencies and intensities of vibronic transitions. Subsequent refinements of the geometry of the lowest excited singlet state are shown to account adequately for the minor differences between experiment and the computational results obtained by using the radical cation as a model for the lowest excited singlet state. From our analysis it also becomes apparent that the excited state is in both molecules subject to vibronic coupling with higher-lying excited states, as exemplified by the presence of transitions to non-totally symmetric vibrational levels. The results of the present study enable the determination of mode-specific reorganization energies accompanying ionization of 1-azaadamantane, which are shown to correspond qualitatively well with those determined in resonance Raman studies on the charge transfer transition in the electron donor-acceptor system 1, which contains 1-azaadamantane as the electron donor unit.
The Journal of Chemical Physics, 2014
We present numerical studies of one-and two-photon excited states ordering in a number of polycyclic aromatic hydrocarbon molecules: coronene, hexa-peri-hexabenzocoronene and circumcoronene, all possessing D 6h point group symmetry versus ovalene with D 2h symmetry, within the Pariser-Parr-Pople model of interacting π-electrons. The calculated energies of the two-photon states as well as their relative two-photon absorption cross-sections within the interacting model are qualitatively different from single-particle descriptions. More remarkably, a peculiar role of molecular geometry is found. The consequence of electron correlations is far stronger for ovalene, where the lowest spin-singlet two-photon state is a quantum superposition of pairs of lowest spin triplet states, as in the linear polyenes. The same is not true for D 6h group hydrocarbons. Our work indicates significant covalent character, in valence bond language, of the ground state, the lowest spin triplet state and a few of the lowest two-photon states in D 2h ovalene but not in those with D 6h symmetry.
The lowest excited singlet state of isolated 1-phenyl-1,3-butadiene and 1-phenyl-1,3,5-hexatriene
The Journal of Chemical Physics, 1992
Vibrationally resolved 1 'A g-2 'A, excitation spectra and decay times for cis,truns-1,3,5,7octatetraene seeded in a supersonic He expansion have been measured by two-color resonance enhanced two-photon ionization spectroscopy. The excitation energy of the 1 'A,-+ 2 'A, O-O band (29 035 cm-') is-6500 cm-' lower than the 35 484 cm-' excitation energy of the 1 'A,-+ 1 'B, O-O band. The intensity pattern of the vibronic development of this spectrum is qualitatively similar to the pattern observed previously in solid state experiments. However, a detailed analysis of the vibrational structure reveals that the electronic structure of the 2 ',4* state is more susceptible to external perturbation than previously suspected. The decay times measured for vibronic levels in the 2 'A, state decrease with increasing vibrational energy, most dramatically for vibrational energies 1200 cm-' and higher. This indicates the increasing importance of a nonradiative decay channel which is most reasonably associated, at least in part, with cis-truns isomerization in the 2 'A, state.