UV-laser induced photo-oxidation of aqueous benzene solutions: Formation of phenol

Aqueous solutions of benzene were irradiated by focussed KrF laser light. The formation of phenol together with varying amounts of 1.3-cyclopentadiene-1-carboxaldehyde was shown by uv absorption measurements. A mechanism for this photo-oxidation via benzene radical cations produced by 2-photon ionization of benzene is proposed. Comparative gas phase laser experiments and experiments with unfocussed laser beams were consistent with previous results using incoherent light sources.     

Multiphoton absorption of broad-band CO2 laser radiation by SF6

Increase of the emission bandwidth of a high-pressure CO₂ laser up to 1.5 cm^–1 increases the multiphoton absorption cross-section of SF₆. Comparison with the previously found [9] increased absorption for shorter pulses suggests that this is also a bandwidth effect. Spectral structures as narrow as 1 cm^–1 above the 10^th absorption step are invoked to explain the observations. The temperature effect, which disappears in the broad-band case, confirms this view.     

Rotational and vibrational temperature determination by DFWM spectroscopy

Using the DFWM technique we determined rotational and vibrational temperatures of NaH molecules in a dynamical system consisting of NaH, Na, H and H₂ for several heat-pipe oven temperatures. We applied a new way to determine the dependence of the DFWM signalI _c ^int on the power of the transition dipole momentµ without previous knowledge of the temperature. The revealed dependence isI _c ^int µ ⁴. In this case the laser intensities were found to be of the same order as the saturation intensity in accordance with simple DFWM theory. A usual Boltzmann plot was employed for the determination of the relevant rotational temperatures, which displayed higher values than the oven temperature.     

New Dunham coefficients of the A 1 ∑ +-State of NaH and NaD

We determined new Dunham coefficients of the A ¹ ∑ ⁺-State of NaH and NaD from degenerate Four- Wave-Mixing (DFWM) spectra in the near UV and in the blue spectral region. In the case of NaH we combined these data with results of Rafi et al. and Orth et al.. The new set of coefficients describes the vibrational dependence of the rotational constants B and D and of the band origins from ? = 0 up to 25. The spectral positions of the lines in our DFWM-spectra can be reproduced by this coefficients with an accuracy better than 0.3 cm^-1 for J-values ≤ 15 and 2 cm^-1 for J-values ≤ 25. Especially for high J-values this is an improvement up to 30 times in comparison to Dunham coefficients recommended before. A RKR-potential of the A ¹ ∑ ⁺-state was calculated with the new coefficients. The Dunham coefficients of NaD were obtained by scaling the NaH coefficients with the reduced masses of the molecules. A comparison of our results to molecular constants determined from the measured NaD-spectra shows good agreement.     

Intercalation of Toluidines into α-Zirconium Hydrogenphosphate

Intercalates of o-, m-, and p-toluidine into α-Zr(HPO₄)₂ · H₂O were prepared and characterized by powder X-ray diffraction, thermogravimetric analysis and infrared spectroscopy. As follows from IR, toludine molecules are protonated in the interlayer space. Toluidine molecules are arranged in a bimolecular way in the intercalates containing more than 1.5 toluidine molecules per Zr atom. On the other hand, a monolayer of the toluidine molecules is supposed in the intercalates with less than one toluidine molecule per Zr atom.     

A statistical model for the fragmentation of benzene by multiphotoionization

A statistical products phase space model for the (multi) photon fragmentation/ionization of polyatomic molecules in strong laser fields is proposed and tested on benzene. The mechanism assumes multiple dissociations and branchings starting with energy rich benzene ions. Calculated and experimental fragment mass patterns versus laser fluence are shown to be in good agreement.     

Degenerate four-wave-mixing spectroscopy in NaH

We performed DFWM spectroscopy on X ^–1+–A ¹⁺ transitions in NaH produced in an indirect photochemical reaction between Na(3p) and H₂ and detected v=1, 2 and 3 ground state vibrational levels of NaH molecules, whereas with resonance enhanced CARS, we observed v=0 levels only. This different sensitivity can be explained by considering the Franck-Condon-factors and the relevant damping coefficients for the corresponding transitions in the NaH molecule. Time resolved DFWM spectroscopy showed that NaH(v=1) molecules effectively live much longer than Na(3p) atoms which merely follow the laser excitation pulse.     

The free energy of a reaction coordinate at multiple constraints: a concise formulation

The free energy as a function of the reaction coordinate (rc) is the key quantity for the computation of equilibrium and kinetic quantities. When it is considered as the potential of mean force, the problem is the calculation of the mean force for given values of the rc. We reinvestigate the PMCF (potential of mean constraint force) method which applies a constraint to the rc to compute the mean force as the mean negative constraint force and a metric tensor correction. The latter allows for the constraint imposed to the rc and possible artefacts due to multiple constraints of other variables which for practical reasons are often used in numerical simulations. Two main results are obtained that are of theoretical and practical interest. First, the correction term is given a very concise and simple shape which facilitates its interpretation and evaluation. Secondly, a theorem describes various rcs and possible combinations with constraints that can be used without introducing any correction to the constraint force. The results facilitate the computation of free energy by molecular dynamics simulations.