The 1612MHz hydroxyl maser in circumstellar envelopes has long been thought to be pumped by 34.6{mu}m photons. Only recently, the Infrared Space Observatory has made possible spectroscopic observations which enable the direct confirmation of this pumping mechanism in a few cases. To look for the presence of this pumping line, we have searched the Infrared Space Observatory Data Archive and found 178 spectra with data around 34.6{mu}m for 87 galactic 1612MHz masers.
Cone search capability for table J/A+A/434/201/table1 (ISO spectral data and OH maser data of the analysed sample of OH-IR sources)
Cone search capability for table J/A+A/434/201/table1a (Observational and derived data for the analysed sample of OH/IR stars with IRAS LRS spectra)