Alkylation Effects on the Energy Transfer of Highly Vibrationally Excited Naphthalene

The energy transfer of highly vibrationally excited isomers of dimethylnaphthalene and 2-ethylnaphthalene in collisions with krypton were investigated using crossed molecular beam/time-of-flight mass spectrometer/time-sliced velocity map ion imaging techniques at a collision energy of approximately 300 cm(-1). Angular-resolved energy-transfer distribution functions were obtained directly from the images of inelastic scattering. The results show that alkyl-substituted naphthalenes transfer more vibrational energy to translational energy than un-substituted naphthalene. Alkylation enhances the V -> T energy transfer in the range -Delta E(d) = -100 similar to-1500 cm(-1) by approximately a factor of 2. However, the maximum values of V -> T energy transfer for alkyl-substituted naphthalenes are about 1500 similar to 2000 cm(-1), which is similar to that of naphthalene. The lack of rotation-like wide-angle motion of the aromatic ring and no enhancement in very large V -> T energy transfer, like supercollisions, indicates that very large V -> T energy transfer requires special vibrational motions. This transfer cannot be achieved by the low-frequency vibrational motions of alkyl groups.