Bridged and linear dilithioacetylenes - Two minima on the potential energy surface?

Vibrational frequency calculations at the 6–31G^*, 6–31G and STO-3G levels in addition to an STO-3G basis set with only a 1s orbital on lithium reveal that both bridged and linear dilithioacetylenes are minima on the potential energy surface.     

Kinetic and analytical study on precipitation reactions with110AgNO3 of some di (β-chloroethyl) amine derivates and hydrochlorides with esters of N-(p-aminobenzoyl)-L-aspartic acid as carriers from dimethylformamide-water solution

The kinetics of precipitation reactions with¹¹⁰AgNO₃ of some di (β-chlorethyl) amine derivates and hydrochlorides with esters of N-(p-aminobenzoyl)-L-aspartic acid as carriers in dimethylformamide-water mixture, were studied. The rate constants of these reactions were of the order of 10^?4 1 · mol^?1 · min^?1. The concentrations of the corresponding hydrochloride solutions were measured by radiometric titration with¹¹⁰AgNO₃ solution of given concentration.     

Improved controlled relative humidity dynamic mechanical analysis of artists’ acrylic emulsion paints

After improvements were made to a modified Polymer Labs MkIII DMTA instrument to facilitate repeatable controlled humidity (RH) experiments using isothermal and thermal scanning conditions, the viscoelastic properties of titanium white pigmented artists’ acrylic emulsion films were measured in tensile mode. The effects of temperature, relative humidity and accelerated ageing regimes on two brands of titanium white paints were explored. These paints are highly responsive to changes in temperature and relative humidity, formulation differences affect properties slightly, and while light ageing had a negligible effect, thermal ageing resulted in decreased storage modulus and increased film density.     

Chirped quantum cascade laser induced rapid passage signatures in an optically thick gas

We report observations of rapid passage signals induced in samples of N₂O and CH₄ present in a multipass cell with an optical path length of 5 m. The effect of laser power and chirp rate upon the signals has been studied by utilising two different chirped quantum cascade lasers operating around 8 μm. The rapid passage signals exhibit an increasing delay in the switch from absorption to emission as a function of increased gas pressure (up to 8 Torr of gas). By comparing a selection of transitions in N₂O and CH₄, we show that, unlike ammonia, this ‘pressure shift’ is independent of the transition dipole moment, spectroscopic branch probed and laser chirp rate. As the transition dipole moment is much larger in nitrous oxide than methane, we believe that this indicates that N₂O–N₂O collisions are more efficient at removing coherence from the polarised sample than CH₄–CH₄ collisions. We have also observed this pressure shift in a short path length of 40 cm, although with a much reduced value, indicating that propagation effects are important in this optically thick minimally damped system.     

Thermally controlled preferential molecular aggregation state in a thiacarbocyanine dye

Herein we report the experimental and theoretical study of the temperature dependence of a thiacarbocyanine dye in its monomer, H- and J-aggregates states. We demonstrate the ability to control the ratio of monomer, H- and/or J-aggregates with heat. We link such a control to the conformation dependence of the molecule. An alternative way to gain access to the dominating species without changing the concentration as a complete switching mechanism between all the present species is proposed. The results presented in this work lead to a better understanding of thiacarbocyanine dye's behavior.