Overview

rotsim2d is a library to model two-dimensional infrared (2DIR) rovibrational spectra. It uses density-matrix perturbation theory treatment of nonlinear spectroscopy 1. It assumes explicit time-ordering of interactions, i.e. it is suitable for time-domain spectroscopy with time-separated optical pulses.

Module rotsim2d.pathways contains classes and functions to produce and manipulate trees of states that represent all possible n^th order dipole excitations starting from some molecular ground state. A specific pathway (a double-sided Feynmann diagram) can be represented by rotsim2d.dressedleaf.Pathway from rotsim2d.dressedleaf, which also allows to calculate the polarization-angular momentum coupling factor for the pathway. An abstract pattern of excitations can be attached to some specific molecular vibrational mode by a rotsim2d.dressedleaf.DressedPathway instance. At this level, one can produce a 2D map of resonance peaks (see rotsim2d.dressedleaf.Peak2D, rotsim2d.dressedleaf.Peak2DList) without calculating line shapes or explicit time dependence.

Module rotsim2d.propagate provides classes and functions for generating actual time-dependent or frequency-domain experimental signals. rotsim2d.visual provides convenience functions to visualize 2D peak maps, 2D spectra and double-sided Feynmann diagrams with LaTeX/TikZ.

Modules rotsim2d.symbolic.functions and rotsim2d.symbolic.results provide SymPy expressions and functions used to derive polarization and angular momentum dependence of four-fold dipole interaction operator.

Actual data on vibrational modes of real molecules is provided by molspecutils package, which (so far) wraps data from the HITRAN database 2.

Footnotes

1

S.Mukamel, “Principles of nonlinear spectroscopy”. Oxford University Press, New York, 1995.

2

I.E. Gordon et al., The HITRAN2016 molecular spectroscopic database, J. Quant. Spectrosc. Radiat. Transfer 203, 3-69 (2017).