Effects of Alkylation on Deviations from Lennard-jones Collision Rates for Highly Excited Aromatic Molecules: Collisions of Methylated Pyridines with HOD

Collision rates and energy transfer distributions are reported for HOD with highly vibrationally excited 2-methylpyridine (2-picoline, E = 38 310 cm(-1)) and 2,6-dimethylpyridine (2,6-lutidine, E = 38 700 cm(-1)). High resolution transient IR absorption is used measured to complete product state distributions of scattered HOD(000) molecules with E-rot = 109 to 1331 cm(-1). Doppler-broadened line profiles characterize the depletion and appearance for HOD molecules due to collisions with hot donors and show that the product translational and rotational energy distributions are similar for both donors with = 370 cm(-1) and similar to 75 cm(-1). The energy transfer rate for picoline (E)/HOD is 2.5 times larger than the Lennard-Jones collision rate. The energy transfer rate for lutidine(E)/HOD is 3.2 times larger than the Lennard-Jones collision rate. Previous work (Havey, Liu, Li, Elioff, and Mullin, J. Phys. Chem. A 2007, 111, 13321-9) reported similar energy transfer values for pyrazine/HOD collisions and an energy transfer rate that is 1.7 times the Lennard-Jones collision rate. The observed collision rates are discussed in terms of hydrogen bonding interactions between HOD and the aromatic donor molecules. Energy gain profiles for HOD are compared with those for H2O.