A COMPUTER-BASED METHOD TO INCREASE THE SIGNAL-TO-NOISE RATIO OF NEGATIVE-ION CURRENTS IN DOUBLE-CHARGE-TRANSFER SPECTROSCOPY

Double-charge-transfer spectroscopy is routinely used to measure doubl e-ionization energies of molecules to singlet and triplet electronic s tates of dications, but is experimentally difficult to apply because t he yield of negative ions generated in the double-electron-capture rea ctions is low, The use of a data-acquisition system and repetitive sca nning of a spectrum can increase signal-to-noise ratios, but the numbe r of scans that can be acquired is limited by drifting in the spectrum position, which results in spectral-peak broadening. This limitation has been overcome in the present investigation by the application of a computer enhancement program that effectively superimposes successive spectra which are subject to slight drift. Spectra obtained for H+ pr ojectile ions reacting with hexafluorobenzene (C6F6) molecules are pre sented; use of the program with such spectra reveals features in the c omputer-enhanced spectrum which are not clearly evident in the individ ual spectra.