Charge @[email protected] processes of the types: or or respectively, occuring in a collision cell (containing a gas, X) located in a field-free region preceding a magnetic and electric sector combination placed in either order, may be detected as follows. If the instrument slits are wide, and if the connections to the two sectors, appropriate to @[email protected] of either positive or negative main-beam ions, are simply reversed, the negative or positive product ions of the two processes, respectively, will be transmitted. If the magnetic field is scanned, a spectrum of such product ions will be obtained, and this spectrum is called a [email protected]@ @[email protected] These spectra are sometimes referred to as −E and +E spectra, respectively. The terms '2E, E/2, −E or +E @[email protected]' should not be used without prior explanation of the meaning 2E, E, +E or −E.