Temperature dependent photoabsorption cross sections of allene and methylacetylene in the VUV-UV region

Using synchrotron radiation as a continuum light source, we have measured t he absolute photoabsorption cross sections of allene (C3H4) and methylacety lene (C3H4) in the respective 130-230 nm and 130-220 nm regions, with a spe ctral bandwidth (FWHM) of 0.06 nm and at three different temperatures, i.e. , 360, 295, and 200 K. Significant temperature effects are observed for bot h molecules in the threshold absorption region. When the gas temperature de creases from 360 to 200 K, the apparent continuum cross sections decrease b y an order of magnitude in the 230 nm region of allene and in the 210 nm re gion of methylacetylene. Within the temperature range of the present work, the presence of hot bands in both molecules are quite limited because of th eir high vibrational frequencies. (C) 2000 Elsevier Science B.V. All rights reserved.