Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

THE SOLID-GAS INTERFACE 24 1Fig. 34. Circuit diagram of an omegatron power supply with constant emission regulator.a shielded box, are subject to crossed magnetic and high frequency electric fields.For a given strength of the magnetic and electric fields, ions of a certain e/M ratiowill spiral along the magnetic lines of force and be trapped by the ion collector.Ions of mass M will be collected whenM = 1.525 Be/F,where B is the magnetic field strength in kilogauss; e is the charge on the ion andF, is the rf frequency in megacycles. The mass range can be scanned by varyingthe magnetic field, or more usually, by varying the rf field. Many other workers haveconstructed and used omegatrons, mainly to monitor vacuum condition^^^^-"^.The kinetics of hydrogerl-deuterium exchange24 and oxygen adsorption"' havebeen studied with this instrument. A disadvantage of the omegatron is thatthe resolution decreases with increasing mass. Although it is extremely sensitivefor the study of hydrogen reactions, adjacent mass numbers higher than 40 arenot well resolved. The large magnet required is a second disadvantage, this mustReferences pp. 270-278