The nature of electron binding in CH3NO2- ions produced by Rydberg electron transfer in K(np)/CH3NO2 collisions is investigated through measurements of the lifetimes and electric-field-induced detachment characteristics of the product ions. The data are interpreted with the aid of recent calculations and by comparison to results obtained using well-known dipole-bound and valence-bound anions. Intercomparison of the various data shows that the observed CH3NO2- ions display the characteristics typical of valence-bound negative ions. This finding is discussed in the light of earlier work on electron binding to CH3NO2. (C) 2003 American Institute of Physics.