| Abstrakt: |
We measured absolute partial cross sections for the formation of all singly charged positive ions formed by electron impact on diborane (B[SUB2]H[SUB6]) from threshold to 200 eV using a time-of-flight mass spectrometer. The absolute total ionization cross section of B[SUB2]H[SUB6] was obtained as the sum of all measured partial ionization cross sections. Dissociative ionization resulting in thirteen different fragment ions was found to be the dominant ionization process, although we found evidence of the presence of the B[SUB2]H[SUP+,SUB6] parent ion. The ion spectrum at all impact energies including in the energy region below 40 eV, which is of special interest for low-temperature plasma technology, is dominated by B[SUB2]H[SUP+,SUB5], B[SUB2]H[SUP+,SUB4] and B[SUB2]H[SUP+,SUB2] fragment ions. The B[SUB2]H[SUP+,SUB5] fragment ion has the largest partial ionization cross section with a maximum value of 2.87 × 10[SUP-16] cm[SUP2] at 60 eV. We also observed H[SUP+], H[SUP+,SUB2], and H[SUP+,SUB3] fragment ions, but no ion signals were found that can be attributed to the formation of doubly charged ions. Additional measurements using a sector-field mass spectrometer revealed that all fragment ions containing one boron atom (B[SUP+], BH[SUP+,SUBy] y = 1-3) and H[SUP+] are formed with significant excess kinetic energy. The mass spectrum of ions formed by electron impact on B[SUB2]H[SUB6] at 70 eV in our experiments revealed distinctly larger abundances of the fragment ions BH[SUP+,SUB3], BH[SUP+,SUB2], and BH[SUP+] than earlier mass spectrometric measurements. [ABSTRACT FROM AUTHOR] |
