Infrared OH absorption lines in 1612 MHz OH maser sources

ISO mid-infrared absorption data helps to distinguish between radiative and collisional pumping mechanisms in 1612 MHz OH masers in various environments. Archive data of OH absorption at 34.6 and 53.3m shows different behavior and different pumping rates for different types of maser sources. © 2008 International Astronomical Union.Acknowledgments This work was partly supported by the Chinese National Science Foundation under Grant No. 10433030 and 10503011