Determination of surface areas by an improved continuous flow method

Abstract

rigid glass at 77 °K (cf Table I). Mirror symmetry was still conserved in all these solvents.There are several centers in the bicyclic ring system where interaction with a polar solvent can be envisaged, with a resultant reduction in the fine structure. This is in accord with a general trend for polar solute molecules in polar and nonpolar solvents (6).The polarity of the solvent influenced the fluorescence quantum yield to a more significant extent than the spectral solvent shifts. The variations extend from a 2-fold increase in Compound 1 to an approximately 10-fold increase in Compound 8. The quantum yields were greatest in benzene and least in DMF or ethanol. The competing excited state processes in operation in these molecules are apparently fluorescence emission (Equation 2), intersystem crossing plus deactivation (Equation 3) and internal conversion from the singlet excited state (Equation 4). iA ii-'A* (1) LA* -2 34A + hv' (2) iA* LA* -LA (3) LA* -iA (4) (6) . H. Jaffe and M. Orchin, "Theory and Applications of Ultraviolet Spectroscopy," John Wiley & Sons, New York, N. Y" 1962, p 186.Permanent photochemical reactions were not observed in these molecules even upon 2-3 weeks of continuous irradiation. The only part triplet states apparently play in these compounds is to provide a possible means of deactivation. Triplet states apparently deactivate quite rapidly as no phosphorescence was observed at 77 °K and the triplet quenchers biacetyl and piperylene were not effective in the transfer of triplet energy. In the case of biacetyl quencher, no biacetyl phosphorescence was observed in thoroughly outgassed solutions of mixtures of a representative series of Compounds 1-12 and biacetyl. In the case of piperylene no cis-trans photostationary state was obtained in Compound 1-piperylene mixture in benzene.The increased solvent polarity enhances the efficiency of internal conversion and/or intersystem crossing relative to fluorescence. The reasons for the increase in relative efficiencies of excited state processes is largely unknown and is an area under intense investigation.

Species identification in visible-ultraviolet vapor spectrometry

“…Table I lists, for a range of wavelengths, e estimated by the three methods detailed in the footnote to the table and a comparison with the published values (5). In only one case was the error in estimating e greater than 10%, even though some observations (3) vapor in equilibrium with liquid (range 273-93 °K) to the normal boiling point (760 Torr at 331.1 °K) (2).…”

“…Figure 3 illustrates data in the temperature range 273-93 °K (where the condensed phase is liquid). The triple point of bromine is at 265.85 °K (2).…”

“…However, anomalous signals have been seen (2), which merge with the true signal, thus limiting the accuracy of low surface area measurements. We have also observed anomalous peaks on a variety of materials and have found that they can be eliminated by proper cell geometry.…”

Determination of low surface areas by the continuous flow method using an interrupted flow technique

“…Sir: In a previous publication (1), we described our improved continuous flow method. A shoulder was sometimes obtained high on the leading edge of the desorption peak.…”

Gas chromatography

“…Burke and Ackerman (150) measured surface areas and adsorption isotherms by frontal analysis with a computer control and data acquisition system. The continuous flow method of surface area measurement was improved by stabilizing the carrier gas flow such that surface areas of 0.1 m2/g or less could be determined (303). A theoretical treatment of continuous countercurrent GC related the column temperature and flow rates for the stationary and mobile phases required for the separation of two component mixtures (38).…”