One Electron Transitions in the Haloforms

The optical absorption o f the halogenated meth­ anes is o f importance because these molecules have been implicated in the depletion o f the tropospheric ozone [1 -4 ]. There is an added interest in the elec­ tronic structure of the halogenated methanes be­ cause o f their industrial use in dry processing and reactive ion etching [5]. Despite the wealth o f data available, all permissible excitations o f electrons from the halogen lone pair to the s, p, and d orbitals have not been observed. In this communication we have reexamined the optical absorption o f the gaseous haloforms using synchrotron radiation, and compared these with previous results [6 -16], The light source for these experiments was the electron storage ring Tantalus at the Synchrotron Radiation Center operated by the University o f Wisconsin, Madison. The gas cell and pumping system have been described in detail elsewhere [5], The light was dispersed by a MacPherson normal incidence m ono­ chromator with a 600 lines/inch grating and trans­ mitted through the cell. The detector was a photo­ multiplier with a sodium salicylate phosphor. In prac­ tice spectra could only be obtained between 2.0 and 11.5 eV photon energy. All spectra were taken via pulse counting into a multichannel data aquisition computer and normalized to a constant photon flux. The photoabsorption spectra for CHC13, CHBr3 and CHI3 are shown in Figure 1. In Table 1 we have summarized our assignments o f the features in our spectra, along with values from the literature which we have used as a guide in making these assign­ ments. Our assignments are in reasonably good agreement with those published elsewhere with a couple of exceptions. We have also included in