Vibrational analysis of the H5O2+ infrared spectrum using molecular and driven molecular dynamics

Standard molecular and driven molecular dynamics are used to analyze prominent spectral features in the H5O2+ infrared spectrum. In the driven method, the molecular Hamiltonian is augmented with a time-dependent term, mu center dot epsilon(0) sin(omega t), where mu is the dipole moment of H5O2+, epsilon(0) is the electric field, and omega is the frequency. The magnitude of the electric field determines whether the driving is mild (the harmonic limit) or strong (anharmonic motion and mode coupling). We analyze the spectrum in the wavenumber range from 600 to 1900 cm(-1), where recent experimental measurements are available for H5O2+. On the basis of the simulations, we have assigned the broad feature around 1000 cm(-1) to the proton transfer coupled with the torsion motion. Intense absorption near 1780 cm(-1) is assigned to the H2O monomer bend coupled with proton transfer.