Temperature Dependence of Absorbance in Ultraviolet Spectra of Organic Molecules V. A. YARBOROUGH, J. F. HASKIN, and W. J. LAMBDIN Carbide and Carbon Chemicals Co., Division o f
Union Carbide and Carbon Corp., South Charleston, W. V a .
weight %). Thus, the instrumental fluctuations and variations in absorbance with ambient temperature exceeded the manipulatory deviations. These variations were not observed, however, when analyses were repeated within intervals of a few minutes. Similar experiments with spectrometric analyses of an aliquot of acetone gave an average daily deviation of only 0.5 weight %. The difference in the behavior of benzene and of acetone may be explained by their temperature coefficients of absorbance. The coefficients for benzene are 0.50 and 0.48% change in absorbance per degree centigrade iii methanol and in iso-octane, respectively; the coefficient for methanol is 0.00 for both diluents. -4~cordingly, quantitstire evaluation of temperature coefficients w : ~ undertaken for other typical organic moleculefi.
The ultraviolet spectra of molecules change with the temperature. Quantitative temperature coefficients of absorbance, however, are not generally available. The variations of ahsorbance with temperature of the sample in the ultraviolet spectra of 19 typical organic compounds have been studied at increments between 5" and 33" C., employing methanol and iso-octane as diluents. The variation ranges from O.Oo/c per ' C. for acetone and 2,Shexanedione to 0.7470 per O C. for toluene. A Car? spectronieter has been fitted with special cells that permit contrnlled 3 ariation of the temperature of the sample.
T
HE absorption spectra of molecules in the ultraviolet spec*tral region are known to change with temperature. Arnold and Kistiakowsky ( 1 ) h a r e observed profound sharpening of the bands exhibited by aromatic compounds when the temperature was lowered to 80" I
