TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Reagent Gas: The reagent gas is methane, isobutane, or ammonia. The ionized reagent gas is mixed with MO compound gas is changed to positive monohydric ion of the form in which H+ carried out one addition to an original molecule, or MO compound gas is changed from an original molecule to positive monohydric ion of the form in which H+ or carried out one elimination or change of both condition is produced. The source gas, MO compound is metalled beta diketone complex comprising dipivaloylmethane (dpm) component or MO compound is metal alkoxide. The average molecular weight of MO compound ion produced is set to M and the average molecular weight of reagent gas is set to R, where a mass selection of MO ion with which a substrate is irradiated is performed within the range of 0.95-1.05 M or within the range more than 2 R. EXAMPLE - Reagent gas, isobutane was ionized by thermoionic emission from a filament by the reagent gas ionization chamber and generated tert-C4H9+ ion. Pb (dpm)2, dipivaloyl methanate (dpm) complex of lead as Mo compound gas was heated at 130degreesC in a container, and sub limited Pb(dpm)2 gas was introduce to the MO ionization chamber by making argon gas into transportation gas. The introduction of tert-c4H9+ ion was carried out through the pore of the grid maintained to the electropositive potential at the MO ionization chamber. Then, tert-c4H9+ ion and pb (dpm)2 were mixed and reacted to produces Pb (dpm)2H+ ion which was stable ion as a gas like original MO compound molecule. There were no solidification and powdering by ionization reaction, and an ion flow can be produced efficiently. The mass separator separated the charged particle by a magnetic field. Pb (dpm)2H+ ion was accelerated by the acceleration deceleration device and an ion beam was formed. A substrate was irradiated with ion beam with 100 electron volts of acceleration energies. Thereby the lead oxide film was obtained with less impurities and with favorable crystallinity.