H Masers at 1720 MHz: Evidence for Shocked Molecular Gas by Dr. Farhad Yusef-Zadeh (Northwestern University)   A new class of OH 1720 MHz masers unaccompanied by main-line transitions have recently been discovered. These masers are associated with supernova remnants (SNRs) interacting with molecular clouds. In this talk I will describe the results of recent radio, millimeter and X-ray observations of supernova remnant masers and discuss their possible correlation with mixed morphology SNRs. These observations support the suggestion that the 1720 MHz OH maser line emission is a powerful shock diagnostic and is collisionally pumped by H2 molecules at the site where C-type supernova shocks drive into adjacent molecular clouds.