Overview
========

`rotsim2d` is a library to model two-dimensional infrared (2DIR) rovibrational
spectra.
It uses density-matrix perturbation theory treatment of nonlinear spectroscopy [#f1]_.
It assumes explicit time-ordering of interactions, i.e. it is suitable for time-domain spectroscopy with time-separated optical pulses.

Module :mod:`rotsim2d.pathways` contains classes and functions to produce and
manipulate trees of states that represent all possible n\ :sup:`th` order dipole
excitations starting from some molecular ground state.
A specific pathway (a double-sided Feynmann diagram) can be represented by :class:`rotsim2d.dressedleaf.Pathway` from
:mod:`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 :class:`rotsim2d.dressedleaf.DressedPathway` instance.
At this level, one can produce a 2D map of resonance peaks (see :class:`rotsim2d.dressedleaf.Peak2D`, :class:`rotsim2d.dressedleaf.Peak2DList`) without calculating line shapes or explicit time dependence.

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

Modules :mod:`rotsim2d.symbolic.functions` and :mod:`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
:external:ref:`molspecutils <molspecutils>` package, which (so far) wraps data from the HITRAN database
[#f2]_.

.. rubric:: Footnotes

.. [#f1] |MUKAMEL|
.. [#f2] |HITRAN|