We have analyzed the fluorescence excitation spectra of carbazole complexes with a single molecule of methyl, deuterated methyl, ethyl, and propyl (1-propanol and 2-propanol) alcohols, cooled in a supersonic jet. We have determined the shifts in the fluorescence excitation spectra of the complexes relative to the frequency of the purely electronic transition of unbound carbazole. They occur as a result of formation of hydrogen bonds between the N-H group of the carbazole and the OH group of the alcohols. The frequencies of stretching vibrations of the hydrogen bonds with different alcohols vary within the range 150-157 cm -1 , while the frequencies of the bending vibrations vary in the range 21-22.9 cm -1 . From the shape of the rotational contours of the bands for the purely electronic and vibronic transitions of the complexes, we determined that they belonged to rotational conformers. We calculated the equilibrium configurations of the complexes in the ground state.Introduction. Complexes formed as a result of hydrogen bonding in a supersonic jet have been studied in a state isolated from the surroundings, and have a controllable composition and a certain equilibrium configuration. Jet cooling of complexes down to a few kelvins ensures resolution of the vibrational structure in the vibronic spectra, which makes it possible to obtain information about the magnitudes of the shifts of the vibrational-rotational absorption and emission bands of the complexes relative to the spectra of the components and about the characteristic lowfrequency vibrations of the hydrogen bond, and to identify conformers of the complexes from the shape of their rotational contours. Carbazole complexes with various gas molecules have been studied to date [1][2][3][4][5].Carbazole complexes with monohydric saturated alcohols have not been studied. Making the alcohol molecule successively more complicated makes it possible to determine the magnitude of the shift in the spectra per methylene group. On the other hand, several rotational conformers of the complex may belong to a given isomer. In a number of cases, they can be identified from the shape of the rotational contours.Experimental Procedure and Calculations. The fluorescence excitation spectra were measured on the automatic spectrometric system described in [2]. The helium carrier gas at a pressure of 2 atm was passed over the surface of the alcohol, which was at a temperature of 233 K to 273 K; the mixture was fed to a prechamber heated to 423 K and containing saturated carbazole vapor. The pulsed supersonic jet was formed by discharge of the ternary gas mixture into the vacuum chamber through a circular nozzle of diameter 0.7 mm. The complexes, cooled down to a few kelvins, were excited perpendicular to the jet axis, at a distance of 19 mm from the nozzle, by the unfocused second-harmonic emission from a frequency-tunable dye laser pumped by the second harmonic of a neodymium-doped yttrium aluminum garnet laser. In recording the rotational contours of the bands, the spectral widt...

UDC 535.37Conformations of He-jet-cooled trimethyl [(3-indole)ethoxy]silane (TIES) have been studied using a laser spectroscopy technique in combination with quantum-chemical computations. Six probable conformers of the molecule were computed, of which only two conformations were observed. Based on an analysis of fluorescence excitation spectra, fluorescence spectra, shapes of rotational band contours at the electronic S 0 -S 1 transition of TIES, and theoretical computations, the above conformers were assigned to steric structures. Twisted structures have the lowest energy due to intramolecular hydrogen bonds C-H⋅⋅⋅O< C Si between hydrogen atoms of methyl groups and an oxygen atom and C-H⋅⋅⋅π between H and the π-electron cloud of the indole ring.Introduction. The non-classical hydrogen bond, interaction between an H atom (bound to one of the electronegative C, O, or N atoms) and the π-electron cloud of an aromatic ring, has been widely studied in the last decade. Such weak non-covalent bonds are formed intramolecularly [1-3] or intermolecularly [4,5] in van-der-Waals complexes in biological systems. Weak H-bonds should be considered when examining molecular structures of fluxional molecules and their stabilization energies. Frequencies of purely electronic S 0 -S 1 -transitions of organic molecular structures vary from units to tens of inverse centimeters [1][2][3]. This makes it possible to use jet cooling to identify these conformers. Various methods of laser UV and IR spectroscopy are used in such investigations. The preferred structures can be determined when they are combined with modern quantum-chemical computation methods.Herein we analyze the molecular structures of trimethyl[(3-indole)ethoxy]silane (TIES) and examine the effect of an intramolecular H-bond on the stabilization energy of its conformers.Experimental. Fluorescence excitation and fluorescence spectra were measured using the automated spectrometry complex that was described before [6]. The carrier gas, He at a pressure of 2 atm, was fed into a prechamber heated to 400 K that contained saturated TIES vapor. The liquid organic compound was placed into capillaries (0.75 internal diameter, 30 mm long). The number of capillaries was selected so that the optimal luminescence signal was obtained. A pulsed supersonic stream was formed by flowing the gas mixture into the vacuum chamber through a round nozzle (diameter 0.7 mm). The cooled molecules were excited by the second harmonic of a frequency-tuned dye laser at distances of 19 and 10 mm from the nozzle for recording fluorescence excitation and fluorescence spectra, respectively. The dye laser was pumped by the second harmonic of a Nd-doped yttrium-aluminum garnet laser (LOTIS TII, LS-2134). The wavelengths of the first harmonic of the dye laser were calibrated using the fluorescence excitation spectrum of iodine vapor. Integral fluorescence was recorded using a Hamamatsu R928 photoelectron multiplier. A DFS-52 monochromator with a diffraction grating (2400 lines/mm) was used to study the fluores...

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