We propose to observe Br_alpha and Br_beta line emission from a sample of
closely-interacting galaxy pairs using ISOSWS. This will provide information
on both the extinction and the ionizing flux in the starbursts contained in
these systems, which may have extinction as high as Av ~ 50.  The data will
be compared with the MIR and FIR maps obtained using ISOCAM and ISOPHT
(approved ISO OT proposal CXU_SS01: "MAPPING IR ENHANCEMENTS IN CLOSELY
INTERACTING SPIRAL-SPIRAL PAIRS"). Our ultimate goal is to answer the
question "how the galaxy-galaxy interactions stimulate the violent starbursts
in colliding galaxy pairs: through disk-disk collision or through
gravitational tidal effects, or both?"