Two-dimensional infrared spectroscopy of neat ice Ih

The assignment of the distinct peaks observed in the OH stretch lineshape of ice Ih is controversial. Recent two-dimensional infrared spectroscopic measurements provided new data. The spectra are, however, challenging to interpret and here we provide simulations that help overcome experimental issues as thermal signals and finite pulse duration. We find good agreement with experiment and the difference between H2O and D2O ices is well accounted for. The overall dynamics is demonstrated to be faster than observed for the corresponding liquid water. We find that excitonic cross peaks exist between the dominant exciton peaks. This leads us to conclude that the cross peaks arise due to the formation of delocalized exciton states, which have essentially no directional correlation between their transition dipoles as opposed to what is commonly seen, for example, in isolated water, where the transition dipoles of the eigenstates are perpendicular to each other.