Lahorija Bistričić

A vibrational assignment of adamantane and some of its isotopomers. Empirical versus scaled semiempirical force field

Abstract Raman and infrared spectra of adamantane-d0 and several of its isotopomers (adamantane-1-d1, adamantane-2-d1, and adamantane-2,2-d2) have been recorded and assigned using the valence empirical force field and isotopic frequency shifts. Few inactive fundamentals of adamantane-d0 were located by means of their activity in either the low-symmetry isotopomers or the low-temperature phase. The vibrational spectrum of adamantane-d16 had to be reinterpreted. The force field obtained from the semiempirical AM1 parametrization was scaled using the vibrational assignments for adamantane-d0, -d16 and -1-d1. The two force fields were compared. Both reproduced the observed frequencies with practically the same average error of 16 cm−1. However, the number of parameters in the scaled semiempirical force field is only nine compared with 27 of the empirical force field.

DFT study of molecular structure and vibrations of 3-glycidoxypropyltrimethoxysilane.

Molecular structure and vibrational frequencies of 3-glycidoxypropyltrimethoxysilane (GPTMS) have been investigated by density functional theory (DFT) calculations using Beckes three-parameter exchange functional combined with Lee-Young-Parr correlation functional (B3-LYP) and standard basis set 6-311++G(d,p). In order to reveal some possible conformations of GPTMS, potential energy scan has been performed in three dihedral angles SiCCC, CCCO and OCCO. The calculations predict the existence of seven different conformations. Raman and IR spectra of liquid samples were recorded and complete assignment of the observed vibrational bands of GPTMS molecule has been proposed. Temperature dependence of Raman spectra between 203K and 293K was examined and vibrational modes characteristic for different conformers were detached.

A density functional theory analysis of Raman and IR spectra of 2-adamantanone

The vibrational force fields for cage-like molecules 2-adamantanone and adamantane were calculated by employing density functional theory (DFT) using 6-31G(d, p) basis set with two nonlocal exchange-correlation functionals BLYP (Becke-Lee-Young-Parr) and the Becke´s three-parameter compound functional B3LYP. DFT infrared intensities and the Raman scattering activities were also calculated to simulate the vibrational spectra. The analysis of the two chosen models show that they are comparable in predicting geometry, vibrational frequencies, IR and Raman intensities. The agreement between the predicted and observed IR and Raman spectra is not satisfactory in the region 1500 - 1200 cm-1 for either of them. The overestimation of the computed intensity connected to the motion of methylene hydrogen atoms is ascribed to the systematic shortcoming of the computational theory. The approach to assignment of the vibrational spectra that combines the comparison of not only calculated and observed frequencies but also of IR and Raman intensities is tested on adamantane and applied to reassignment of the normal modes of 2-adamantanone. The scale factors for the force constants of the C=O group were derived. The scaled BLYP and B3LYP force fields reproduced the experimental frequencies of 2-adamantanone with an average error of 12 cm-1 and 10 cm-1, respectively. The error in reproducing the experimental frequencies of adamantane is 13 cm-1 (BLYP).

Influence of proton irradiation on the structure and stability of poly(dimethylsiloxane) and poly(dimethylsiloxane)-nanodiamond composite

In the present study, pure poly(dimethylsiloxane) (PDMS) polymer and PDMS-detonation nanodiamond (PDMS-DND) composite with 1wt.% of DND were irradiated under vacuum at room temperature with a 2MeV proton beam with fluences in the 1013–1015cm−2 range. Modification of the structures and properties of the pure polymer and the nanocomposite material were monitored as a function of proton fluence. Specifically, the vibrational dynamics of pure PDMS and PDMS-DND nanocomposites, both unirradiated and irradiated samples, were investigated using Raman and Fourier transform infrared spectroscopy (FTIR). The Raman and FTIR spectra of the PDMS and PDMS-DND composites exhibit an overall reduction in intensity of all vibrational bands of the irradiated samples. The changes in relative intensities of the characteristic vibrational bands as a function of irradiation fluence indicate that cleavage of the backbone (Si–O–Si) PDMS chains was most pronounced. Importantly, structural degradation of PDMS-DND composites takes pl...

The envelope of projectile trajectories

The paper presents yet another elegant solution to the classical problem of maximizing the range of a projectile fired from above or from below the horizontal target plane. The method makes use of the envelope of the family of the projectile trajectories and it not only solves the original problem, but can be applied to maximize the projectile range on a target surface of arbitrary shape. Three different ways of deriving the equation of the envelope are shown. As an example the range of a projectile is maximized on a parabolic target surface. The envelope can also be used to minimize the kinetic energy of a projectile given the target point.

Vibrational analysis of 2-adamantanone and its deuterated isotopomers

Abstract The vibrational analysis of 2-adamantanone and the group of all possible mono- and two gem-dideuterated 2-adamantanone isotopomers (2-adamantanone-3-d1, 2-adamantanone-endo-4-d1, 2-adamantanone-exo-4-d1, 2-adamantanone-5-d1, 2-adamantanone-6-d1, 2-adamantanone-4,4-d2 and 2-adamantanone-6,6-d2) is presented. The assignments for fundamentals are based on the characteristic group frequencies, i.e. comparison with adamantane, Raman depolarization ratios, isotopic frequency shifts and are supported by the normal coordinate calculations. The force field was obtained from the semiempirical AM1 calculations and the assumed transferability of the scaling factors for adamantane. The average error between the observed and calculated frequencies is 11 cm−1. The effects of the carbonyl group and deuterium substitutions on the adamantane-like normal modes were investigated in terms of the harmonic mode scrambling analysis.

Raman study of vibrational dynamics of aminopropylsilanetriol in gas phase

Raman spectrum of aminopropylsilanetriol (APST) in gas phase has been recorded at room temperature in macro chamber utilizing two-mirror technique over the sample tube. Unlike predominantly trans molecular conformation in condensed phase, the spectra of vapor show that the molecules are solely in gauche conformation with intramolecular hydrogen bond N···HO which reduces the molecular energy in respect to trans conformation by 0.152 eV. The assignment of the molecular spectra based on the DFT calculation is presented. The strong vibrational bands at 354 cm(-1), 588 cm(-1) and 3022 cm(-1) are proposed for verifying the existence of the ring like, hydrogen bonded structure. Special attention was devoted to the high frequency region, where hydrogen bond vibrations are coupled to stretchings of amino and silanol groups.