# Method development for geometric functions pt 3: $$\beta$$ aligned-frame (AF) parameters with geometric functions.

• 01/09/20 v2 with verified AF code.

• 09/06/20 v1

Aims:

• Develop $$\beta_{L,M}$$ formalism for AF, using geometric tensor formalism as already applied to MF case.

• Develop corresponding numerical methods - see pt 1 notebook.

• Analyse geometric terms - see pt 1 notebook.

## $$\beta_{L,M}^{AF}$$ rewrite

The various terms defined in pt 1 can be used to redefine the full AF observables, expressed as a set of $$\beta_{L,M}$$ coefficients (with the addition of another tensor to define the alignment terms).

The original (full) form for the AF equations, as implemented in ePSproc.afblm <https://epsproc.readthedocs.io/en/dev/modules/epsproc.AFBLM.html>__ (note, however, that the previous implementation is not fully tested, since it was s…l…o…w… the geometric version should avoid this issue):

\begin{eqnarray} \beta_{L,-M}^{\mu_{i},\mu_{f}} & = & \sum_{l,m,\mu}\sum_{l',m',\mu'}(-1)^{M}(-1)^{m}(-1)^{(\mu'-\mu_{0})}\left(\frac{(2l+1)(2l'+1)(2L+1)}{4\pi}\right)^{1/2}\left(\begin{array}{ccc} l & l' & L\\ 0 & 0 & 0 \end{array}\right)\left(\begin{array}{ccc} l & l' & L\\ -m & m' & S-R' \end{array}\right)\nonumber \\ & \times & I_{l,m,\mu}^{p_{i}\mu_{i},p_{f}\mu_{f}}(E)I_{l',m',\mu'}^{p_{i}\mu_{i},p_{f}\mu_{f}*}(E)\\ & \times & \sum_{P,R,R'}(2P+1)(-1)^{(R'-R)}\left(\begin{array}{ccc} 1 & 1 & P\\ \mu_{0} & -\mu_{0} & R \end{array}\right)\left(\begin{array}{ccc} 1 & 1 & P\\ \mu & -\mu' & R' \end{array}\right)\\ & \times & \sum_{K,Q,S}(2K+1)^{1/2}(-1)^{K+Q}\left(\begin{array}{ccc} P & K & L\\ R & -Q & -M \end{array}\right)\left(\begin{array}{ccc} P & K & L\\ R' & -S & S-R' \end{array}\right)A_{Q,S}^{K}(t) \end{eqnarray}

Where $$I_{l,m,\mu}^{p_{i}\mu_{i},p_{f}\mu_{f}}(E)$$ are the energy-dependent dipole matrix elements, and $$A_{Q,S}^{K}(t)$$ define the alignment parameters.

In terms of the geometric parameters, this can be rewritten as:

\begin{eqnarray} \beta_{L,-M}^{\mu_{i},\mu_{f}} & =(-1)^{M} & \sum_{P,R',R}{[P]^{\frac{1}{2}}}{E_{P-R}(\hat{e};\mu_{0})}\sum_{l,m,\mu}\sum_{l',m',\mu'}(-1)^{(\mu'-\mu_{0})}{\Lambda_{R'}(\mu,P,R')B_{L,S-R'}(l,l',m,m')}I_{l,m,\mu}^{p_{i}\mu_{i},p_{f}\mu_{f}}(E)I_{l',m',\mu'}^{p_{i}\mu_{i},p_{f}\mu_{f}*}(E)\sum_{K,Q,S}\Delta_{L,M}(K,Q,S)A_{Q,S}^{K}(t)\label{eq:BLM-tidy-prod-2} \end{eqnarray}

Where there’s a new alignment tensor:

\begin{equation} \Delta_{L,M}(K,Q,S)=(2K+1)^{1/2}(-1)^{K+Q}\left(\begin{array}{ccc} P & K & L\\ R & -Q & -M \end{array}\right)\left(\begin{array}{ccc} P & K & L\\ R' & -S & S-R' \end{array}\right) \end{equation}

And the the $$\Lambda_{R',R}$$ term is a simplified form of the previously derived MF term:

\begin{equation} \Lambda_{R'}=(-1)^{(R')}\left(\begin{array}{ccc} 1 & 1 & P\\ \mu & -\mu' & R' \end{array}\right)\equiv\Lambda_{R',R'}(R_{\hat{n}}=0) \end{equation}

All phase conventions should be as the MF case, and the numerics for all the ternsors can be used as is… hopefully…

Further notes:

• Note $$B_{L,S-R'}(l,l',m,m')}$$ instead of $$B_{L,-M}(l,l',m,m')}$$ for MF case. This allows for all MF projections to contribute.

Refs for the full AF-PAD formalism above:

1. Reid, Katharine L., and Jonathan G. Underwood. “Extracting Molecular Axis Alignment from Photoelectron Angular Distributions.” The Journal of Chemical Physics 112, no. 8 (2000): 3643. https://doi.org/10.1063/1.480517.

2. Underwood, Jonathan G., and Katharine L. Reid. “Time-Resolved Photoelectron Angular Distributions as a Probe of Intramolecular Dynamics: Connecting the Molecular Frame and the Laboratory Frame.” The Journal of Chemical Physics 113, no. 3 (2000): 1067. https://doi.org/10.1063/1.481918.

3. Stolow, Albert, and Jonathan G. Underwood. “Time-Resolved Photoelectron Spectroscopy of Non-Adiabatic Dynamics in Polyatomic Molecules.” In Advances in Chemical Physics, edited by Stuart A. Rice, 139:497–584. Advances in Chemical Physics. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2008. https://doi.org/10.1002/9780470259498.ch6.

Where  has the version as per the full form above (full asymmetric top alignment distribution expansion).

### To consider

• Normalisation for ADMs? Will matter in cases where abs cross-sections are valid (but not for PADs generally).

### Status

TODO: more careful comparison with experimental data (see old processing notebooks…)

## Setup

:

# Imports
import numpy as np
import pandas as pd
import xarray as xr

# Special functions
# from scipy.special import sph_harm
import spherical_functions as sf
import quaternion

# Performance & benchmarking libraries
# from joblib import Memory
# import xyzpy as xyz
import numba as nb

# Timings with ttictoc or time
# https://github.com/hector-sab/ttictoc
from ttictoc import TicToc
import time

# Package fns.
# For module testing, include path to module here
import sys
import os
modPath = r'D:\code\github\ePSproc'  # Win test machine
# modPath = r'/home/femtolab/github/ePSproc/'  # Linux test machine
sys.path.append(modPath)
import epsproc as ep
# TODO: tidy this up!
from epsproc.util import matEleSelector
from epsproc.geomFunc import geomCalc

* pyevtk not found, VTK export not available.

:

from IPython.core.interactiveshell import InteractiveShell
InteractiveShell.ast_node_interactivity = "all"

:

# Plotters
import matplotlib.pyplot as plt
from epsproc.plot import hvPlotters
hvPlotters.setPlotters()