Gas-phase deprotonation of arylalkylamines. A collision-induced dissociation study

The collision-induced dissociation (CID) of deprotonated arylalkylamines of general formula R(1)C(6)H(4)CHR(2)CH(2)NR(3)(2) (where R(1) = H, OH, F or NO(2); R(2) = H or OH; R(3) = H or CH(3)) generated by negative chemical ionization with H(2)O and D(2)O as ionizing reagents, is discussed. The negative chemical ionization mass spectra show that, in the absence of a hydroxy group in the aromatic ring, deprotonation takes place at the benzylic position whereas the proton is lost from the OH group when present. The nitro compound forms only M(-.) ions. The CID spectra of the deprotonated molecules show that fragmentations are strongly dependent on the structural features of the molecules, namely the presence or absence of substituents in the aromatic ring or aliphatic chain. Copyright 1999 John Wiley & Sons, Ltd.     

The onset of coulomb explosions in polyatomic molecules

With the development of high intensity femtosecond lasers, the ionisation and dissociation dynamics of molecules has become an area of considerable interest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and benzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 nm). Results are presented and contrasted for laser beam intensities around 10(15) and 10(16) W cm(-2). For the lower intensities, the mass spectra yield dominant singly charged parent ions. Additionally, the appearance of doubly charged parent ions is evident for carbon disulphide, toluene and benzaldehyde with envelopes of doubly charged satellite species existing in these local regions. Carbon disulphide also reveals a small triply charged component. Such atomic-like features are thought to be a strong fingerprint of FLMS at these intensities. However, upon increasing the laser intensity to approximately 10(16) W cm(-2), parent ion dominance decreases and the appearance of multiply charged atomic species occurs, particularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly ionised parent species which can subsequently blow apart. Copyright 1999 John Wiley & Sons, Ltd.     

Uniform molecular analysis using femtosecond laser mass spectrometry

The potential of femtosecond laser time-of-flight mass spectrometry (FLMS) for uniform quantitative analysis of molecules has been investigated. Various samples of molecular gases and vapours have been studied, using ultra-fast ( approximately 50 fs) laser pulses with very high intensity (up to 1.6 x 10(16) Wcm(-2)) for non-resonant multiphoton ionisation/tunnel ionisation. Some of these molecules have high ionisation potentials, requiring up to ten photons for non-resonant ionisation. The relative sensitivity factors (RSF) have been determined as a function of the laser intensity and it has been demonstrated that for molecules with very different masses and ionisation potentials, uniform ionisation has been achieved at the highest laser intensities. Quantitative laser mass spectrometry of molecules is therefore a distinct possibility. Copyright 1999 John Wiley & Sons, Ltd.     

Quantum-Chemical Modeling of the Effect of Stretching Mechanical Activation of the Central С–С Bonds in Linear Polymers

Russian Journal of Physical Chemistry A - The effect of mechanical activation by preliminarily stretching linear polymeric hydrocarbon molecules (e.g., polyethylene and polypropylene) on the energy...     

Some Dynamic Properties of the Interface

Russian Journal of General Chemistry - By means of an original technique, two dynamic effects at the interface, viscoelasticity and spreading, were considered. The first effect was studied with the...     

Phase transitions and crystal-field and exchange interactions in TbFe3(BO3)4 as seen via optical spectroscopy

High-resolution polarized broadband (1800-23?000?cm(-1)) optical absorption spectra of Tb(3+) in TbFe(3)(BO(3))(4) single crystals are studied between room temperature and 4.2?K. The spectral signatures of the structural (R32-P3(1)21, T(S )?=?192?K) and magnetic (T(N )?=?41?K) phase transitions are found and analyzed. Energies and symmetries of the Tb(3+) crystal-field (CF) levels were determined for both the high-temperature R32 and the low-temperature P3(1)21 structures of TbFe(3)(BO(3))(4) and compared with the calculated ones. It follows unambiguously from the spectral data that the ground state is the Γ(1)?+?Γ(2) quasi-doublet of the local D(3) point symmetry group for Tb(3+) in the R32 high-temperature structure. The CF calculations revealed the CF parameters and wavefunctions for Tb(3+) in TbFe(3)(BO(3))(4). The value of the Tb-Fe exchange integral and of the effective magnetic field created by the ordered Fe subsystem were estimated as J(fd)?=?0.26?K and B(eff)?=?3.92?T, using the observed splitting Δ?=?32?cm(-1) of the Tb(3+) ground quasi-doublet at the temperature 5?K. The reliability of the obtained parameters was proven by modeling the literature data on the magnetic susceptibility of TbFe(3)(BO(3))(4). Lattice distortions below T(S) were evidenced by the observed changes of probabilities of the forced electric dipole transitions of Tb(3+).     

Exawatt-Zettawatt pulse generation and applications

A new amplification method, weaving the three basic compression techniques, Chirped Pulse Amplification (CPA), Optical Parametric Chirped Pulse Amplification (OPCPA) and Plasma Compression by Backward Raman Amplification (BRA) in plasma, is proposed. It is called C³ for Cascaded Conversion Compression. It has the capability to compress with good efficiency kilojoule to megajoule, nanosecond laser pulses into femtosecond pulses, to produce exawatt-and-beyond peak power. In the future, C³ could be used at large-scale facilities such as the National Ignition Facility (NIF) or the Laser Megajoule (LMJ) and open the way to zettawatt level pulses. The beam will be focused to a wavelength spot size with a f#1. The very small beam size, i.e. few centimeters, along with the low laser repetition rate laser system will make possible the use of inexpensive, precision, disposable optics. The resulting intensity will approach the Schwinger value, thus opening up new possibilities in fundamental physics.     

Modeling macromolecular movement in polymer melts and its relation to nonlinear rheology

We present direct evidence of the macromolecular network behavior at high deformation rates based on macroscopic simulation of these systems by a group of elastics as a model of flexible-chain polymer concentrated solutions or melts. It was shown that at low deformation rates, the disentanglement process really takes place providing a possibility to irreversible deformations (flow), while at high deformation rates, the dominating effect is the formation of large inhomogeneous structures (??grains?? or ??bundles??) consisting of flocks of entangled chains. This is a model of the deformation induced flow-to-rubbery transition, which makes the irreversible flow impossible. The attempt to increase the deformation rate leads to the rupture of elastics. So, we constructed a model for the deformation-induced fluid-to-rubber transition at high rates and confirmed it by direct measurements of elastic-to-plastic strain ratio as a function of deformation rate.     

Illumination of the effect of the overlap of lone-pairs on indirect nuclear spin-spin coupling constants

The effect of electron lone-pairs on the Fermi-contact (FC) contribution to indirect nuclear spin-spin coupling constants is analyzed using new tools for their interpretation. In particular, visualization of spin-spin coupling pathways using the coupling deformation density (CDD) has been employed. Furthermore, the recently developed perturbation-stable localization procedure has been applied for decomposition of CDD and the calculated value of couplings into contributions from localized molecular orbitals (LMOs). Correlation between the overlap of densities of LMOs representing lone-pairs and the Fermi-contact contribution to spin-spin coupling constants has been demonstrated. A new way for analyzing spin-spin couplings using the expansion of CDD as a linear combination of the products of molecular orbitals has been suggested. The considered examples include two- and three-bond phosphor-phosphor couplings. Significance of the obtained insight is not restricted to spin-spin couplings of nuclei possessing lone-pairs, as demonstrated in the example of vicinal hydrogen-hydrogen coupling in ethane.