The dynamics of the
reactions CH
3
+ HBr → CH
4
+ Br and HO
+ HBr → H
2
O + Br have been
studied using the quasiclassical trajectory method to explore the
interplay of the vibrational excitation of the breaking bond and the
potential energy surface characterized by a prereaction van der Waals
well and a submerged barrier to reaction. The attraction between the
reactants is favorable for the reaction, because it brings together
the reactants without any energy investment. The reaction can be thought
to be controlled by capture. The trajectory calculations indeed provide
excitation functions typical to capture: the reaction cross sections
diverge when the collision energy is reduced toward zero. Excitation
of reactant vibration accelerates both reactions. The barrier on the
potential surface is so early that the coupling between the degrees
of freedom at the saddle point geometry is negligible. However, the
trajectory calculations show that when the breaking bond is stretched
at the time of the encounter, an attractive force arises, as if the
radical approached a HBr molecule whose bond is partially broken.
As a result, the dynamics of the reaction are controlled more by the
temporary “dynamical”, vibrationally induced than by
the “static” van der Waals attraction even when the
reactants are in vibrational ground state. The cross sections are
shown to drop to very small values when the amplitude of the breaking
bond’s vibration is artificially reduced, which provides an
estimate of the reactivity due to the “static” attraction.
Without zero-point vibration these reactions would be very slow, which
is a manifestation of a unique quantum effect. Reactions where the
reactivity is determined by dynamical factors such as the vibrationally
enhanced attraction are found to be beyond the range of applicability
of Polanyi’s rules.
The previously widespread mercury cell technology in chlorine production has now been replaced by more environmentally friendly membrane cell electrolysis which is a Best Available Techniques (BAT) technology. However, this requires a much cleaner brine containing contaminants (Al, Ca, Mg, etc.) in the order of ng/g at most. For this reason, it’s very important to detect trace amounts of aluminum in concentrated saline media in the simplest and fastest way. To the best of our knowledge, no one has previously developed a spectrophotometric method capable of detecting aluminum in ionic forms selectively in the order of ng/g in concentrated saline media, without any preconcentration or separation step. Our advanced analytical method provides an opportunity for this. During the analytical procedure, a colored complex ion is formed from the dissolved aluminum content of the sample with eriochrome cyanine R (ECR) ligand in buffered pH medium. The sensitivity of the measurement is increased by adding quaternary ammonium salt. The colored complex ion is formed in 15 minutes, then the absorbance measurement can be performed for 90 minutes. The effect of rock salt interference was eliminated by proper calibration. In our work the dependence of the signal on temperature, pH, time elapsed after the addition of reactants, the dosing sequence, the salinity of the medium was examined, furthermore, we studied which wavelength-absorbance values give the best fit (highest R2 value) and the highest sensitivity in case of linear calibration. Surprisingly, increasing the salinity significantly improves the sensitivity of the measurement.
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