Isotopic effects on the dynamics of the CH3(+) + H2 → CH5(+) → CH3(+) + H2 reaction.

Diffusion Monte Carlo is used to investigate the anharmonic zero-point energy corrected energies for the CH(3)(+) + H(2)→ CH(5)(+) → CH(3)(+) + H(2) process as a function of the center of mass separation of the two fragments. In addition to the title reaction, all possible deuterated and several tritiated (CH(4)T(+) and CH(3)T(2)(+)) analogues of this reaction are investigated. As anticipated, the replacement of one or more of the hydrogen atoms with deuterium or tritium atoms lowers the zero-point energy of the system.

Theoretical investigations of mode mixing in vibrationally excited states of CH5+.

Using diffusion Monte Carlo, five vibrational excited states of CH(5)(+) and CD(5)(+) are evaluated and analyzed. Here, we focus on the fundamentals in the five modes that are generated by requiring that the wave functions change sign at specified values of the five symmetry-adapted linear combinations (SALCs) of the CH or CD bond lengths. Even though the definitions of these modes are based on displacements of the CH or CD bond lengths, the frequencies are found to be low compared to previously calculated CH vibrational frequencies in this molecule.

Characterizing excited states of CH5+ with diffusion Monte Carlo.

The spectroscopy and dynamics of protonated methane have been of long-standing interest due to the unusual and highly fluxional behavior of CH5+. This reflects the fact that the ground-state wave function for CH5+ has nearly equal amplitude at the 120 equivalent minima and at the saddle points that connect these minima. While low-resolution spectra of CH5+ have been assigned, the nature of the couplings between the CH stretches and the low-frequency modes is not as well characterized.

Vibrational dynamics of carboxylic acid dimers in gas and dilute solution.

Ultrafast mid-IR transient absorption spectroscopy has been used to study the vibrational dynamics of hydrogen-bonded cyclic dimers of trifluoroacetic acid and formic acid in both the gas and solution phases (0.05 M in CCl(4)). Ultrafast excitation of the broad O-H cyclic dimer band leads, in the gas phase, to large-scale structural changes of the dimer creating a species with a distinct free O-H stretching band on 20 ps and 200 ps timescales.