The vibrational spectra of the elementoorganic starburst dendrimers

The main features of vibrational spectra of starburst dendrimers have been analyzed for the first time. Their spectral pattern, in general, is determined by the ratio of a number of terminal groups to a number of repeating units. This ratio tends to m_r−1 (m_r — branching functionality of repeating unit), and becomes constant, when the generation number of the starburst dendrimer increases higher than 3-5. IR and Raman spectra of twelve generations of the phosphorus-containing dendrimers are represented and interpreted on the basis of the calculation of frequencies of the normal vibrations and band intensities in the IR spectra of ‘molecules’ terminated by dangling methyl groups, which are the fragments of the dendrimer molecule. Tailored spectra of these fragments are then compared with experimental spectra and satisfactory similarity has been obtained. Experimental spectra of generations higher than 4 are very similar, according to the theoretical approach. The results can be used for the analysis of the chemical and physical transformations in starburst dendrimers.     

Multidimensional anharmonic calculation of the vibrational frequencies and intensities for the trans and cis isomers of HONO with the use of normal coordinates

The equilibrium geometry and the potential energy and dipole moment surfaces have been determined for the cis and trans isomers of the HONO molecule by an ab initio Moller–Plesset (MP2) calculation with a wide set of atomic orbitals. The multidimensional anharmonic vibrational Schrodinger equations are solved using the variational method with the Hamiltonian and wave functions written in the normal coordinates of cis and trans isomers. All one- and two-dimensional and a number of three-dimensional vibrational problems are solved to obtain the energy levels and vibrational eigenfunctions. The frequencies and intensities for the fundamental, overtone and some combination bands are determined in good agreement with the available experimental results. The calculation shows the strength of coupling between different vibrational modes and reveals the presence of strong resonances between the (v₁, v₃, v₆) and (v₁, v₃−1, v₆+2) states of cis-HONO. This fact may be important for understanding the energy redistribution between the intermolecular degrees of freedom. The magnitude and direction of vibrationally averaged ground-state dipole moment of both isomers, as well as the direction of transition dipole moments, are in good agreement with the experimental findings. The changes in the values of dipole moment and some geometrical parameters of cis- and trans-HONO on vibrational excitation are also computed.     

Intensity distribution in the bands of the B1 → X1Σ+ system of PbO

Relative intensities of a few bands of the B1→X¹Σ⁺ system of PbO have been measured by the technique of heterochromatic photographic photometry. The Franck-Condon factors andr-centroids have been computed by the more reliable numerical integration procedure, using a suitable potential. The effective vibrational temperature of the source is found to be 3836 K.     

A quantitative study of diffracted X-ray intensities from type I natural diamond crystals by high resolution X-ray diffractometry and comparison with nearly perfect silicon single crystals

Results of accurate measurements of peak and integrated intensities of , 111 and 333 reflections of natural diamonds of type I and nearly perfect silicon single crystals are reported. Highly monochromated and collimated MoK _{α 1} exploring beam was used. A quadrupole crystal X-ray diffractometer was employed in (+, −, +) and (+, −, +, −) settings. (111) platelets of diamond and silicon crystals with thicknesses of about 1 mm were selected. High resolution diffraction curves, stationary and traverse topographs were recorded. Diffraction curve half widths of diamond and silicon crystals were in the range: 45–200 arc sec and a few arc sec respectively. The experimental values of integrated intensitiesρ for diamond crystals were found to lie between the theoretical values for ideally perfect and ideally imperfect crystals. Experimental values ofρ for silicon were closer to the “perfect crystal” values. This is consistent with the results of diffractometric and topographic evaluation. The peak intensities of all reflections were higher for diamond crystals in comparison to the silicon crystals. The ratioI _C/I _Si lies in the range 1.3 (111 reflection) to 10.5 and (333) reflections. This is anomalous and cannot be accounted for by considering the degree of perfection, structure factor and difference in absorption coefficient.     

Conformational behaviour and vibrational spectra of 3-methyl 2-butanethiol

The Raman spectra of 3-methyl 2-butanethiol in the temperature range-120° C to + 60° C have been recorded together with its liquid phase infrared spectrum at room temperature. The spectral analysis shows that the molecule of the compound exists in the liquid state, in three different rotameric configurationsA, B andC of which the formA is the stablest. Besides, a tentative assignment of the observed vibrational frequencies arising from the rotameric forms has been presented.     

3d D lifetime in laser cooled Ca : Influence of cooling laser power

We have measured the lifetime of the metastable 3D _5/2 level in Ca⁺ using the “quantum jump" technique on a single stored and laser cooled ion in a linear Paul trap. We found a linear dependence of the measured decay rate on the power of the laser which repumps the ions from the long lived 3D _3/2 level. This can be explained by off-resonant depletion of the 3D _5/2 level. The proper lifetime of this level is obtained by a linear extrapolation of the measured lifetime to zero laser power. We obtain 1100(18) ms in agreement with theoretical calculations. The observed systematic change of the decay rate resolves discrepancies between earlier experiments in which this effect had not been considered. Measurements on a linear chain of 10 laser cooled ions showed unexpected frequent coincidences of quantum jumps within our observation time of 20 ms. This indicates a so far unexplained correlation between the ions in the chain at large distances. Received 3 March 1999     

Temperature Dependence of Integrated Intensities of Vibrational Bands in M2GeF6 IR-Absorption Spectra

The paper presents experimental results of studies on the temperature dependence of integrated intensities of vibrational bands corresponding to ₃(GeF ₆) in M₂GeF₆ IR-spectra. It is shown that unlike Na₂GeF₆, Rb₂GaF₆, and Cs₂GeF₆, where the dependence of intensity on temperature is monotonous, in the case of K₂GeF₆ there exist anomalous temperature ranges of 220-240 and 150-170 K, where the intensity of a band, corresponding to ₃(GeF^2- ₆) changes abruptly. The study of heat evaluation, heat capacity, unit cell parameters, and intensities of selective reflexes in K₂GeF₆ X-ray diffraction patterns indicates the presence in this compound, as distinguished from others in the seris considerod, of phase transitions of the first order. On the basis of IB, ¹⁹F NNR, X-rat and calorimetric data, a possible mechanism of polymorphic transformation is discussed.     

Variation of Dipole Moment Function of O-H Bond of t-Butanol with the Nature of Solvent and Its Temperature

The intermolecular influence on dipole moment function is evaluated for O-H bond of t-butanol in different nonpolar solvents at temperatures ranging from 10° to 60°C employing IR band intensities of fundamental and first overtone bands. Two sets of dipole moment derivatives have been calculated corresponding to – and +- combinations of the transition moment matrix elements R₁₀ and R₂₀, the values for ++ and -+ combinations are equal in magnitude to those for - and +- combinations, respectively and opposite in signs. In general the dipole moment derivatives increase on lowering the temperature as well as with increasing molecular interactions with the solvent molecules. Dipole moment plots with dimensionless coordinate ξ [=(r-r_e)/r_e, where r and r_e are internuclear distances during vibration and at equilibrium, respectively] are reported for various systems considered. It is found that for +- combination the dipole moment maximum shifts to higher internuclear distances when polarisation of the solute molecules is increased by lowering of temperature or increase in molecular interactions between solute and solvent molecules. A reverse trend is observed for – combination.- The OH band of t-butanol vapor has been measured.     

Line intensities of the asymptotic asymmetric-top radical HO2 at high temperatures

The total internal partition sums were calculated in the product approximation at temperatures up to 5000 K for the asymptotic asymmetric-top HO2 molecule. The calculations of the rotational partition function and the vibrational partition function were carried out with the rigid-top model and in the harmonic oscillator approximation, respectively. Our values of the total internal partition sums are consistent with the data of HITRAN database with -0.14% at 296 K. Using the calculated partition functions, we have calculated the line intensities of υ2 band of HO2 at several high temperatures. The results showed that the calculated line intensities are in very good agreement with those of HITRAN database at temperatures up to 3000 K, which provides a strong support for the calculations of partition functions and line intensities at high temperatures. Then we have extended the calculation to higher temperatures. The simulated spectra of υ2 band of the asymptotic asymmetric-top HO2 molecule at 4000 and 5000 K are also obtained.     

New line intensity measurements for C2H2 around 7.7 μm and HITRAN format line list for applications

Absolute intensities of 467 lines are measured in 9 bands of the 7.7 μm spectral region of the ¹²C₂H₂ molecule, with an average accuracy of 5%. For each band, the vibrational transition dipole moment squared and Herman-Wallis coefficients are obtained in order to model the rotational dependence of the transition dipole moment squared. These results are used to calculate a line list for atmospheric or astrophysical applications. Merged in the line list set up in a previous work for the 8 strongest bands around 7.7 μm [5], these new data give now a quasi-exhaustive view of the ¹²C₂H₂ spectrum in the involved spectral region.