The most widely used correction of fluorescence intensities for inner filter effects in conventional (90 degrees ) fluorimeters fails at high absorbance values. We have critically examined this failure, which is caused by the difference between the geometrical parameters (GPs) of the excitation and emission beams in the typical instrument (focused beams) and in the theoretical picture on which the correction is based (collimated beams). We provide two types of experimental measurement of GPs and show that their substitution in the correction equations leads to significant improvements in the linear range of corrected fluorescence. We also demonstrate that mathematical optimizations give greater improvements and that the optimizations yield GPs consistent with experimental measurements. For solutions exhibiting primary inner filter effect only, we have extended the range of linearity of corrected fluorescence to a(ex) (absorbance per cm) up to 5.3; for systems with both primary and secondary inner filter effects we have achieved linearity for a(ex) + a(em) = 6.7. In all cases linear fits have slopes which agree well with the dilute limit. Different series of one- and two-solute solutions were used to demonstrate effectiveness of our correction methods. We also provide a rationale for the unexpected independence of GPs on excitation and emission bandwidths.

The "solvation" of a H3+ molecule-ion by H2 molecule(s) and/or a He atom was examined in ab initio electronic structure calculations. Binding energies and geometrical parameters were determined for the ground electronic states of H"+ ( = 3,5,7,9,11) and HeH"+ ( = 3, 5,7,9) cluster ions. Floating spherical Slater orbitals (FSSO) were employed with full single and double configuration interaction (Cl). All of the clusters studied were found to be weakly bound (with respect to removal of "solvent" species). Inclusion of configuration interaction had a major effect; for > 5, it increased the energy required to remove an H2 molecule from H"+ by ~35% and that to remove the He atom from HeH"+ by ~300-400%. The net solvation energy per H2 (~3.5 kcal mol"1 for the first three solute molecules, ~1.5 kcal mol'1 for the fourth) was found to be about threefold larger than for He.

Ab initio calculations have been performed at the MP2/6-31G** level for the series of fluorinated ethanes, C 2 H n F 6-n , n ) 0-5. The resulting geometries, dipole moments, vibrational frequencies, and absolute infrared intensities are reported for stable conformers of the series, including both anti and gauche species, together with their energy differences, for 1,2-difluoroethane, 1,1,2-trifluoroethane, and 1,1,2,2-tetrafluoroethane. The results are compared to available experimental data. In particular, because of the importance of members of this series as potential CFC substitutes, the accuracy of the computational results for infrared frequencies and intensities is discussed, including the dependence on basis set, for calculations at the MP2 level of the theory.

A supersonic free jet expansion was used to prepare van der Waals complexes of the type I2NeaHeb. Complexes containing as many as seven rare gas atoms were identified as satellites in the fluorescence excitation spectrum of the I2 B (v′=13 to 26) ←X (v″=0) band system by their relative dependence on the concentrations of neon and helium. For a+b?6, the frequencies of the van der Waals satellites follow a simple band shift rule: ν (I2NeaHeb) =ν (I2)+Aa+Bb, where A and B are weak functions of the I2 vibrational state. This observation, along with the failure of the rule for I2Ne7, provide some information concerning the geometry and binding in these molecules. Progressions (w′=0,1, and 2) in van der Waals modes of I2Ne and I2NeHe were also identified. The problem of intramolecular energy transfer was studied by observation of the dispersed emission spectra of the I2* fragments produced upon laser-induced photodissociation of these complexes. The product vibrational state distributions could be determined by using the known Franck–Condon factors and the observed intensities of the iodine transitions. All complexes required at least one I2 stretching quantum per rare gas atom for complete dissociation. Larger species favored dissociation channels involving more than one vibrational quantum per rare gas atom.