Their method uses x-rays, in the form of x-ray photoelectron spectroscopy. (pnnl.gov)
Using X-ray photoelectron spectroscopy and Fourier transform infrared imaging, the team found carbonyl groups at the tail ends of the polymer chains. (scientificamerican.com)
DeVine et al. used photoelectron spectroscopy to discern the quantum mechanical underpinnings of this 1,2 shift in a prototypical case: conversion of vinylidene (H2CC) to acetylene (HCCH). (science.sciencemag.org)