Richard M. Hedges

Methylenecyclobutane: Ring‐Puckering Potential Function from Mid‐Infrared Combination Bands

The mid‐infrared spectra (4000–250 cm−1) of methylenecyclobutane, methylene‐d2‐cyclobutane‐2,2‐d2, and methylene‐d2‐cyclobutane‐d6 have been examined closely for the occurrence of combination bands involving the ring‐puckering vibration. A progression of sum bands for methylenecyclobutane and a progression of difference bands for methylene‐d2‐cyclobutane‐2,2‐d2 have been simultaneously fit by the one‐dimensional potential function in the ring‐puckering coordinate x: V(x) = 4.229 × 105x4 − 1.694 × 104x2. This potential function yields a barrier of 168 ± 10 cm−1 at the planar conformation, in good agreement with the barrier of 160 ± 40 cm−1 determined by other workers from the vibrational dependence of the rotational constants in the microwave spectrum. The detailed shape of the function does not agree as well and particularly the failure of the infrared function to account for the observed 0–1 splitting is noted. This had been noted earlier in the case of silacyclobutane and to a lesser degree, in the case...

Electronic states of azulene and naphthalene calculated by CNDO/2 CI

Abstract Transition energies and oscillator strengths were calculated for the singlet and triplet states of azulene and naphthalene within the CNDO/2 CI framework. The calculated phosphorescent radiation lifetimes for naphthalene and azulene are 14 seconds and 260 seconds, respectively.

S1 and S2 fluorescence of fluoranthene

Abstract The fluorescence from the first two excited singlet states of fluoranthene in rigid glass at 77 K has been observed and characterized as to its wavelength and time behavior. The S 1 fluorescence occurs over the region from 4050 A to approximately 5400 A with a typical lifetime of 58 ns. The S 2 fluorescence occurs in region from 3700 A to 3950 A with a typical lifetime of 143 ns. In each region short lived lines (with lifetimes of from 5 to 34 ns) are observed which are interpreted as occurring from unrelaxed excited vibrational levels of the excited electronic states.

Vibrational spectra of methylenecyclopentane, methylenecyclopentane-2,2,5,5-d4 and methylene-d2-cyclopentane-2,2,5,5-d4

Abstract The 42 fundamental frequencies of methylenecyclopentane, methylenecyclopentane-2,2,5,5-d4 and methylene-d2-cyclopentane-2,2,5,5-d4 are assigned from the vapor and liquid phase infrared spectra and the Raman spectra of liquid samples. Assignments are made on the basis of group frequencies, intensities, isotopic shifts, gas phase band contours, Raman depolarization ratios and comparison with similar molecules. The lowest frequency ring mode is observed as a combination band progression in the mid-infrared spectrum of methylenecyclopentane yielding a progression of bands beginning at 158.0 cm−1 and decreasing in frequency. These bands are interpreted in terms of a one-dimensional harmonic vibration with a small negative quartic anharmonicity. This interpretation is favored over that of pseudorotation in the methylenecyclopentane molecule.

Energy transfer from the second excited singlet state of spirobifluorene

Energy transfer from the second excited state of spirobifluorene is examined by polarization spectroscopy. Evidence against spiroconjugation and evidence in favor of a coulombic mechanism is reviewed and discussed. This coulombic interaction is categorized as an intramolecular energy transfer caused by the ‘extrinsic factors’ of the Weber nomenclature.

THEORETICAL CALCULATIONS OF SINGLET–SINGLET AND SINGLET–TRIPLET RADIATIVE LIFETIMES IN AROMATIC HYDROCARBONS

Abstract CNDO/2—CI calculations have been made for the molecules benzene, naphthalene, azulene, biphenylene, anthracene, and phenanthrene. Transition energies and oscillator strengths are given for several of the lowest energy singlets and triplets of the π,π* states and the three lowest σ,π excited states of the several molecules. The phosphorescence radiative lifetimes are given also.

Crystal field theory with covalency

The use of a covalency parameter in Crystal Field Theory calculations has been applied to sixteen octahedral complexes. The variables fitted to experiment have been correlated to theoretical parameters.ZusammenfassungKristallfeld-Berechnungen mit einem Kovalenz-Parameter werden an sechzehn oktaedrischen Komplexen durchgeführt. Die dem Experiment angepaßten Variablen wurden mit theoretischen Parametern in Beziehung gesetzt.

The electronic structure of angular polyphenes

SCF calculations of molecular orbitals and electronic transition energies for angular polyphenes of two through nine benzene rings have been made. The calculated sequences of the singlet and triplet energies of the α, β, β′, and p bands (Clars notation) are compared to the limited available experimental data.ZusammenfassungPPP-Rechnungen mit begrenzter Konfigurationenwechselwirkung wurden für die Reihe der angular anellierten Polyphene durchgeführt. Die berechneten α-, β-, β′- und p-Banden werden mit den wenigen vorhandenen experimentellen Daten verglichen.RésuméCalculs SCF des orbitales moléculaires et des énergies de transition électronique pour les polyphenés angulaires de deux à neuf cycles benzeniques. Les séries calculées pour les énergies singulet et triplet des bandes α-, β-, β′ et p (notation de Clar) sont comparées aux quelques données expérimentales disponibles.