Quantum Theoretical Studies Research Articles

Spectroscopic and quantum theoretical studies of species with metal-to-metal bonus

The background and qualitative features of M-M bonds of orders 3 to 4 are reviewed . Attention is then given to the quantitative calculation of the electronic structures of such bonds and the correlation of the theoretical results with experimental observations, especially spectroscopic ones. The results of SCF-Xa-SW calculations for the [Re 2Cl 8] 2− ion, including relativistic corrections, are presented. The relativistic effects shift the energies of filled and virtual molecular orbitals with substantial Re atomic contributions by several thousand wavenumbers. Hence, such corrections are essential in assigning the observed spectra. The earlier assignment of the [Re 2Cl 8] 2− spectrum is revised in several ways on the basis of the new calculations. Finally, the spectrum of the Mo 2[(CH 2) 2P(CH 3) 2] 4 molecule at 5°K is reported and the abundant vibrational structure in the δ→δ * ( 1A 2u← 1A 1g) transition discussed. The analysis shows that we are dealing here with a beautiful example of mixing of conventional vibronic (Herzberg-Teller) excitation and tne anomalous involvement of a totally symmetric vibration in vibronic coupling due to the intrinsic weakness of the dipole-allowed intensity, a phenomanon observed earlier by Martin, Newman, and Fanwick in Mo 2(O 2CCH 3) 4.

Possible existence and role of excited ozone precursors in the stratosphere

Laboratory kinetic experiments, quantum theoretical studies and certain recently discovered infrared emissions from the stratosphere together imply the possible existence of a metastable, energetic, and reactive form of ozone in the upper atmosphere. This species can potentially affect the upper atmospheric photochemistry and heat balance. For these reasons there is a need for further quantum theoretical and laboratory chemical kinetic studies addressing some of the relevant properties of the internally excited ozone precursors.

Some color naming experiments for red and green monochromatic lights.

Instability in the color appreciation of monochromatic flashes for a normal trichromat is studied with respect to the instability in the stimulus due to the statistical fluctuation in the number of incident quanta and the distribution of this number over the retinal receptors. The frequencies of reddish, yellowish, greenish, bluish, colorless, white, etc., appearances in the perception were determined under variation of brightness, wavelength, exposure time, and area of the test stimulus. By comparison with the quantum theoretical studies conducted previously for absolute threshold values, it is found that for green excitation, three quanta, and for red, two quanta are required for a colored perception. For the long wave end two systems are sensitive, a “red” and a “colorless” system. In the green two quanta excitations result in colorless appearances of the perception.