Low energy electron spectroscopy of N2 in the 11.8–13.8 eV energy range

In the 11.8–13.8 eV energy range differential threshold and energy loss spectra of electrons scattered by N₂ molecules have been obtained at an incident energy of 14.3 eV and with a 30 meV experimental resolution. The study of the angular behaviour of the observed peaks permits us to distinguish between singlet-singlet and singlet-triplet transitions. The predicted F³Π_u and G³Π_u Rydberg states are observed. Also some levels of unknown triplet states are seen at 13.155, 13.395 and 13.635 eV.     

Forbidden character in electronic spectra of mono-halonaphthalenes

The singlet-singlet absorption and emission spectra of α-fluoro and the absorption spectra of α-chloro-, α-iodo-, and β-bromo-naphthalenes have been photographed and analyzed. The absorption spectra of all the four molecules show the presence of two discrete systems of bands, and the emission spectrum of α-fluoronaphthalene corresponds to the longer-wavelength system of absorption. With the α-chloro- and α-iodo-naphthalenes, the longer-wavelength system shows the appearance of pure electronic transition with weak bands, while the corresponding transitions in case of α-fluoro- and β-bromo-naphthalenes appear with the most intense bands of the system, as expected theoretically. The appearance of strong vibronic and weak electronic bands in the longer-wavelength system of the former two molecules has been interpreted as the interaction of totally symmetric vibrations, a rare example in the literature.     

Isotope shifts in spectra of molecular liquids

In the IR absorption spectra of low-temperature molecular liquids, we have observed anomalously large isotope shifts of frequencies of vibrational bands that are strong in the dipole absorption. The same effect has also been observed in their Raman spectra. At the same time, in the spectra of cryosolutions, the isotope shifts of the same bands coincide with a high accuracy (±(0.1–0.5) cm^–1) with the shifts that are observed in the spectra of the gas phase. The difference between the spectra of examined low-temperature systems is caused by the occurrence of resonant dipole–dipole interactions between spectrally active identical molecules. The calculation of the band contour in the spectrum of liquid freon that we have performed in this work taking into account the resonant interaction between states of simultaneous transitions in isotopically substituted molecules can explain this effect.     

Theoretical analysis of the MCD spectra of some singlet-triplet transitions in formaldehyde

A recently developed theoretical treatment of the magneto-optical activity of singlet-triplet transitions in molecules which are near-symmetric rotors is employed in simulation of the MCD spectra associated with some singlet-triplet transitions in formaldehyde. The theoretical results are compared with the relevant experimental data, and the agreement between theory and experiment is found to be satisfactory.     

Photoacoustic Spectroscopic Studies of Mono-Substituted Naphthalene Molecules

The present paper deals with the Photoacoustic (PA) studies of mono-substituted (hydroxy) naphthalene molecules, namely 1-naphthol and 2-naphthol in boric acid glass in the region 250–400 nm. The electronic transitions of these molecules observed experimentally, have been interpreted using the optimised geometries and CNDO/S-CI method. Assignments of observed electronic transitions are made on the basis of singlet-singlet and singlet-triplet transitions. The PA spectra of 1-naphthol and 2- Maphthol are compared with its parent molecule i.e. naphthalene molecule, in terms of charge transfer character of -OH group and polarization of molecules. It is observed that the non-radiative transitions in mono-substituted naphthalene molecules shift towards the higher wavelength region when compared with naphthalene molecule, which may be attributed to increase in the charge density in the substituted ring.     

Triplet-triplet absorption spectra of quinoline and isoquinoline

The difference between the singlet-singlet and the triplet-triplet absorption spectra of quinoline and isoquinoline has been measured from 45 000 to 15 000 cm^?1, in a rigid hydrocarbon glass at 77 K, using a newly constructed computer controlled spectrograph. Both molecules show strong new triplet-triplet absorption bands in the ultraviolet region. Similar bands have recently been found in naphthalene and were assigned to transitions from the lowest triplet state to a triplet state which is doubly excited with respect to the closed shell ground state.     

Spectral-Luminescence Characteristics of Carbazole, Dibenzofuran, and Dinaphthofuran in the Gas Phase in Excitation by Electrons and Photons

The spectra of electron-energy loss, the excitation functions, and the fluorescence spectra in excitation of carbazole, dibenzofuran, and dinaphthofuran by monoenergetic beams of electrons of different energies are determined. The singlet-triplet transitions S ₀–T ₁ and the singlet-singlet transitions up to S ₀–S ₇ are recorded, which covers the region 2–11 eV. In the spectra of electron-energy loss, bands that refer to the n^ast and ^* transitions are identified. The replacement of the heteroatom of nitrogen by the atom of oxygen in the five-membered ring has no substantial effect on the spectra of electron-energy loss.     

Inner-shell excitation of formaldehyde,acetaldehyde and acetone studied by electron impact

Excitation and ionisation of the carbon and oxygen 1s electrons of formaldehyde, acetaldehyde and acetone have been examined by small-angle inelastic scattering of 2.5-keV electrons, with energy resolutions in the range 0.20–0.50 eV FWHM. Features in the electron energy loss spectra below the inner-shell ionisation thresholds have been assigned to transitions to unoccupied valence (π*) and Rydberg orbitals. Broad maxima in the inner-shell continua of all three molecules have been interpreted as resonances associated with transitions to σ*(CO) orbitals. The assignments of the acetaldehyde and acetone spectra have been supported by comparison with those for CH₄ and H₂ CO. The adiabatic first ionisation potential of H₂ NO and H₂ CF have been estimated from the inner-shell spectra of formaldehyde using the equivalent-core analogy.     

Specific effects of a polar solvent in optical absorption spectra of 5,12-tetracenequinone

We have measured the optical absorption spectra of 5,12-tetracenequinone (5,12-naphthacenequinone) in polar protic (methanol) and nonpolar (n-hexane) solvents. It has been shown that shifts of some bands in the polar solvent compared to the nonpolar one are caused by the formation of high hydrogen bonds between methanol molecules and the molecules under study. The occurrence of hydrogen bonds leads to changes in the energy gaps between occupied and unoccupied molecular orbitals of 5,12-tetracenequinone and, as a consequence, to corresponding changes in energies of electronic transitions. Based on analysis of the absorption spectra in different solvents in combination with the data of calculations of electronic spectra and taking into account changes in the orbital pattern under the action of the solvent, we have determined exact electronic configurations of electronically excited singlet states of 5,12-tetracenequinone.     

Interaction of Electrons with Indole,Tryptophan, and their Derivatives in the Gas Phase

The electron energy loss spectra (EELS) of indole, 3-indolyl propionic acid, 3-indolealdehyde, 3-dimethylaminomethylindole, tryptophan, and N-acetyl-L-tryptophan in the gas phase upon excitation by monokinetic electrons with an energy of E₀ = 11–50 eV are obtained. The structure of EELS is determined in the main by the indole chromophore; the side groups, except for the C=O group of 3-indolealdehyde, exert an insignificant influence. The energy of the lower triplet level ³L_a is 3.3 eV for indole and its derivatives and 3.2 eV for tryptophan and N-acetyl-L-tryptophan. Four singlet transitions in the region of 4.4–7.2 eV have been identified. The molecules studied, except for tryptophan, fluoresce in the gas phase on excitation by electrons. At low values of E₀ (10–25 eV), the fluorescence spectra are similar and are due to the indole fluorophore. Just as in the case of optical excitation, fluorescence on excitation by electrons is associated with the ¹L_b-S₀ transitions. An increase in the energy E₀ up to 60–80 eV leads to dissociation of a portion of the indole molecules and to the appearance of additional bands in the fluorescence spectrum. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 4, pp. 468–472, July–August, 2005.