  For organic molecules adsorbed as well-oriented ultra-thin films on metallic
surfaces, angle-resolved photoemission spectroscopy has evolved into a
technique called photoemission tomography (PT). By approximating the final
state of the photoemitted electron as a free electron, PT uses the angular
dependence of the photocurrent, a so-called momentum map or k-map, and
interprets it as the Fourier transform of the initial state's molecular
orbital, thereby gains insights into the geometric and electronic structure of
organic/metal interfaces.
  In this contribution, we present kMap.py which is a Python program that
enables the user, via a PyQt-based graphical user interface, to simulate
photoemission momentum maps of molecular orbitals and to perform a one-to-one
comparison between simulation and experiment. Based on the plane wave
approximation for the final state, simulated momentum maps are computed
numerically from a fast Fourier transform of real space molecular orbital
distributions, which are used as program input and taken from density
functional calculations. The program allows the user to vary a number of
simulation parameters such as the final state kinetic energy, the molecular
orientation or the polarization state of the incident light field. Moreover,
also experimental photoemission data can be loaded into the program enabling a
direct visual comparison as well as an automatic optimization procedure to
determine structural parameters of the molecules or weights of molecular
orbitals contributions. With an increasing number of experimental groups
employing photoemission tomography to study adsorbate layers, we expect kMap.py
to serve as an ideal analysis software to further extend the applicability of
PT.
