H3+, the simplest polyatomic molecule, plays a key role in dense interstellar clouds as the initiator of ion-molecule chemistry. The detection of H3+ in diffuse interstellar clouds came as a surprise, however, and suggested a serious (factor of ~100) problem in the simple model of diffuse cloud chemistry. In particular, this observation raised questions as to the applicability of laboratory measurements of the H3+ dissociative recombination rate to interstellar conditions. We have recently measured the dissociative recombination rate of rotationally cold H3+ ions in an ion storage ring, and have also detected H3+ in the classical diffuse cloud towards Zeta Persei, where the electron fraction is known from previous observations. This combination of new laboratory measurements and astronomical observations has eliminated two of the primary uncertainties in the chemical model, and implies a previously unrecognized and significant enhancement in the cosmic-ray ionization rate in the diffuse interstellar medium.
Tuesday, May 17th
Seminar is to be held at 4:00 PM in the conference room
on the second floor of Dearborn Observatory
Refreshments will be served at 3:30
|
