Bressan, GiovanniGiovanniBressanvan Thor, Jasper JJasper Jvan Thor2021-07-012021-07-012021-06-28The Journal of Chemical Physics, 2021, 154 (24), pp.1-100021-9606http://hdl.handle.net/10044/1/89993Two-dimensional vibrational and electronic spectroscopic observables of isotropically oriented molecular samples in solution are sensitive to laser field intensities and polarization. The third-order response function formalism predicts a signal that grows linearly with the field strength of each laser pulse, thus lacking a way of accounting for non-trivial intensity-dependent effects, such as saturation and finite bleaching. An analytical expression to describe the orientational part of the molecular response, which, in the weak-field limit, becomes equivalent to a four-point correlation function, is presented. Such an expression is evaluated for Liouville-space pathways accounting for diagonal and cross peaks for all-parallel and cross-polarized pulse sequences, in both the weak- and strong-field conditions, via truncation of a Taylor series expansion at different orders. The results obtained in the strong-field conditions suggest how a careful analysis of two-dimensional spectroscopic experimental data should include laser pulse intensity considerations when determining molecular internal coordinates.© 2021 Author(s). This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in J. Chem. Phys. 154, 244111 (2021); https://doi.org/10.1063/5.005143502 Physical Sciences03 Chemical Sciences09 EngineeringChemical PhysicsJournal Articlehttps://www.dx.doi.org/10.1063/5.0051435https://aip.scitation.org/doi/10.1063/5.0051435RPG-2018-3721089-7690