Negative ion formation from photoexcited carbon tetrachloride and silicon tetrachloride studied by negative-ion mass spectrometry in the range of 12.4-31.0Â eV

Negative ion formation from photoexcited carbon tetrachloride (CCl4) and silicon tetrachloride (SiCl4) has been investigated by negative-ion mass spectrometry using synchrotron radiation in the energy range of 12.4-31.0 eV. Only Cl− anions are detected in a negative ion mass spectrometer. Negative ion yields for the Cl− anion were measured in terms of the photon energy. We observe a variety of photochemical processes relevant to the electronic states of the molecules. Assignments of peaks were made on the basis of the thermochemical data and fragment ion appearance energy reported previously. The onset at ∼14.9 eV in the negative ion yield curve of CCl4 presumably corresponds to the Rydberg state (converging to the C˜,T22 limit) giving rise to consecutive fragmentation of photoexcited CCl4 leading to CCl2++Cl−+Cl. Similarly, the onset at ∼15.9 eV in SiCl4 presumably corresponds to the Rydberg states (converging to the D˜,A21 limit) leading to the ion-pair formation mainly involving SiCl2++Cl−+Cl.