Measurement of Negative Ions Formed by Electron Impact. IV. Negative Ion Mass Spectra and Ionization Efficiency Curves of Negative Ions of m/e 17 and 16 from n-Propyl and Isopropyl Alcohols

The negative ion mass spectra of n- and iso-propyl alcohols, with emphasis on their relative yields to the positive ions under 80 eV, 40 eV and 15 eV electron energies, and the ionization efficiency (IE) curves of OH− and O− ions to the extent of 50 eV electron energies were measured. In both cases, the electron impacts of 80 eV and 40 eV gave almost the same negative ion mass spectra, in which the relatively strong peaks of m⁄e 16 (O−), m⁄e 17 (OH−) and m⁄e 25 (C2H−) ions except for the decrement of C2H− ions in 40 eV for isopropyl alcohol were characteristic. For n-propyl alcohol, the ratio of the yield of CH2OH+ ions to that of O− ions (CH2OH+/O−) gave the values of 6.9×104 and 1.9×105 in 80 eV and 40 eV. For isopropyl alcohol the values of C2H4OH+/OH− were 3.3×104 and 6.4×104 in 80 eV and 40 eV, respectively. The comparison of the yield of negative ion in 10 eV with that of positive ion in 15 eV gave CH2OH+/O−=2.0×104 and C2H4OH+/OH−=2.3×103. Each appearance potential observed in IE curves is well interpreted by the following reactions. [OH− ions], for the first process C3H7OH(n- or iso-)+ e−→OH−+ C2H4+CH2+H, for the second process C3H7OH(n- or iso-)+ e−→OH−+CH3+CH2+CH2++e− or OH−+C2H4+CH2+H+e−. [O− ions], for the first process C3H7OH(n- or iso-)+e−→O−+C2H5+CH3, for the second process C3H7OH(n- or iso-)+e−→O−+C2H4+CH3+H or O−+C2H3+CH3+H2 and for the third process C3H7OH(n- or iso-)+ e−→O−+C3H7(n-or iso)+H++e− or O−+C3H5+H2+H++e−.