  We investigated 64 pairs of interacting-CME events identified by the
simultaneous observations of SOHO and STEREO spacecraft from 2010 January to
2014 August, to examine the relationship between the large SEP events in the
energy of 25-60MeV and the properties of the interacting CMEs. We found that
during CME interactions the large SEP events in this study were all generated
by CMEs with the presence of enhanced type II radio bursts, which also have
wider longitudinal distributions comparing to events with the absence of type
II radio burst or its enhancement (almost associated with small SEP events). It
seems that the signature of type II radio bursts enhancement is a good
discriminator between large SEP and small or none SEP event producers during
CME interactions. The type II radio burst enhancement is more likely to be
generated by CME interactions, with the main CME having larger speed (v),
angular width (WD), mass (m) and kinetic energy (E_k), that taking over the
preceding CMEs which also have higher v, WD, m and E_k, than those preceding
CMEs in CME pairs missing the type II radio bursts or enhancements. Our
analysis also revealed that the intensities of associated SEP events correlate
negatively with the intersection height of the two CMEs. Most of
type-II-enhanced events and SEP events are coincidentally and almost always
made by the fast and wide main CMEs that sweeping fully over a relatively
slower and narrower preceding CMEs. We suggest that a fast CME with enough
energy completely overtaking a relatively narrower preceding CME, especially in
low height, can drive more energetic shock signified by the enhanced type II
radio bursts. The shock may accelerate ambient particles and lead to large SEP
event more easily.
