EXPLORING MOLECULES IN EXTREME ENERGY STATES: COLLISIONAL RELAXATION AND PHOTODISSOCIATION OF ACTIVATED MOLECULES

Abstract

This dissertation presents studies that explore how molecules behave when prepared in extreme energy states. A new state-resolved high-resolution transient IR absorption spectrometer paired with a tunable UV excitation source was constructed for the majority of the work.

In the first study, collisional deactivation of pyrazine (E_vib=37900 cm-1) with NH3 is characterized with a full state distribution of NH3(0000) products. NH3-pyrazine collisions are found to have modest energy gains with T_trans=400–650 K and T_rot=480±80 K. There is a limit on V-RT energy gain with T_trans decreasing as E_rot^ of the NH3 product increases which suggests impulsive collisions for the V-RT energy pathway. The total appearance rate constant of NH3(0000) is half the collision rate constant showing that there is significant contribution from the V-V energy pathway.

The second study investigates strong CO2-collidine (E_vib=39100 cm-1) collisions. The distribution of CO2(J =58-78) are reported and compared to other methylpyridines. While the state density of 2,6-lutidine is three orders of magnitude lower than 2,4,6-collidine, they have similar J-dependent translational temperatures and the rotational temperatures are within error. Integrated rate constants for CO2(J =60-78) increase as a function of donor molecule size. The integrated rate constant more than doubles from 2,6-lutidine to 2,4,6-collidine. Donor size decreases the energy transferred per collision but increases the probability of collisional energy transfer.

For last study, tunable UV excitation (λ=212-220 nm) is used to investigate the photodissociation mechanism of SO2 from the C ̃ state. Measurement of the SO products yield rotational distributions, energy partitioning, quantum yields, and action spectra. SO(v=0) products show an average 4 times more translation than rotation. SO(v=1) product branching ratio was 2% of the total SO products and showed a similar preference for translation. There are equal populations of the three F manifolds across the entire range of UV excitation. Preference for translational energy in the SO(v=0) and SO(v=1) products, low SO(v=1) population, and equal F manifold population indicate SO2 dissociates via coupling to a repulsive triplet state near threshold.