The results of the attenuation studies were also confirmed +1 by studying the cross section vs. beam energy curves for the B ( S) and +3, B ( P) In these studies the measured appearance potentials were used to infer certain molecular properties. In general, the electron. it may.provide into the nature of the process that leads to electron fragmentation of mol ecules but also, from a more practical point in preparing ionsfor, use in: ion-mo'lecule studies since in the latar case it is.,necessaryto know the electronic state of the projectile ion in order to infer quantitative information on a reaction under study. We have, therefore, 2.undertaken a study of the electronic states of B produced by electron bombardment of the boron trihalides using the attenuation of the B+ ion beam in a suitable gas as a function of the target gas pressure as a diagnostic tool. It was found that the fraction of the excited electronic + state present in the B beam varied in a systematic way as one varied the target gas in the series ranging from BF3 to BI3. In addition, some preliminary measurements of the cross sections of certain ion-molecule reactions were made and found to be consistent with the conclusions drawn from the attenuation studies.Experimental Method and Procedure 'The apparatus used in this work has been described previously and it consists of a 180° magnetic sector mass spectrometer with a 1 cm radius of curvature in tandem with a 60° magnetic sector with an 8 in.radius of curvature. Detection of product ions is realized by counting the ions with a 17 stage electron multiplier. Gas pressures were measured wit an MI