Temperature dependence of collisional deactivation of highly vibrationallyexcited biphenylene

Collisional energy transfer between highly vibrationally excited biphenylen e and a variety of mono- and polyatomic bath gases has been measured at tem peratures between 333 and 523 K. Biphenylene molecules were initially prepa red with an additional vibrational energy of 28 490 cm(-1) by electronic ab sorption at 351 nm followed by fast internal conversion. The collisional de activation was observed by detection of the energy dependent UV absorption at the red edge of the strong band at 255 nm. A carefully tested empirical energy calibration, based on high temperature shock tube data was used. A n egative temperature dependence of [Delta E], referred to Lennard-Jones coll ision numbers Z(LJ) was found for the vibrational energies between 10000 an d 30000 cm(-1) in all rare gases, N-2, CO2, SF6, ethane, butane and heptane as colliders. This temperature dependence is only very weak in light ran g ases and increases systematically with the efficiency of the collider. The absolute values of [Delta E] are analyzed in comparison with recent data se ts on related larger polyatomic molecules and with results of trajectory ca lculations. In the discussion of the measured temperature dependence the pr oblems with a proper distinction between the T-dependence of [Delta E] and of the collision number are also addressed.