  We theoretically calculate the electron impact partial and total ionization
cross sections of R-carvone $(\mathrm{C_{10}H_{14}O})$, 2-butanol
$(\mathrm{C_{4}H_{10}O})$, imidazole $(\mathrm{C_3H_4N_2})$ and
2-nitroimidazole $(\mathrm{C_3H_3N_3O_2})$. We have used the Binary Encounter
Bethe (BEB) model to obtain the total electron impact ionization cross sections
(TICS). The modified BEB method in combination with mass spectrum data of the
molecules is used to calculate the partial ionization cross sections (PICS) of
the cationic fragments dissociating from the parent molecule. Our PICS data for
R-carvone and 2-butanol are in good agreement with the experimental data for
all the cation fragments along with the TICS data. For imidazole and
2-nitroimidazole, the estimates of the PICS are reported for the first time in
the present study. We have found that both the modified BEB method and the mass
spectrum dependence method work effectively to estimate PICS if we have
information about the appearance energies and relative abundance data of the
target under investigation.
