Computer spectrometers

Dattani, Nikesh S.

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https://hdl.handle.net/2142/96957 Copy

Description

Title

Computer spectrometers

Author(s)

Dattani, Nikesh S.

Issue Date

2017-06-19

Keyword(s)

Comparing theory and experiment

Abstract

"Ideally, the cataloguing of spectroscopic linelists would not demand laborious and expensive experiments. Whatever an experiment might achieve, the same information would be attainable by running a calculation on a computer. Kolos and Wolniewicz were the first to demonstrate that calculations on a computer can outperform even the most sophisticated molecular spectroscopic experiments of the time, when their 1964 calculations of the dissociation energies of H$_2$ and D$_{2}$ were found to be more than 1 cm$^{-1}$ larger than the best experiments by Gerhard Herzberg, suggesting the experiment violated a strict variational principle. As explained in his Nobel Lecture, it took 5 more years for Herzberg to perform an experiment which caught up to the accuracy of the 1964 calculations._x000d_ _x000d_ Today, numerical solutions to the Schr\""odinger equation, supplemented with relativistic and higher-order quantum electrodynamics (QED) corrections can provide ro-vibrational spectra for molecules that we strongly believe to be correct, even in the absence of experimental data. Why do we believe these calculated spectra are correct if we do not have experiments against which to test them? All evidence seen so far suggests that corrections due to gravity or other forces are not needed for a computer simulated QED spectrum of ro-vibrational energy transitions to be correct at the precision of typical spectrometers. Therefore a computer-generated spectrum can be considered to be as good as one coming from a more conventional spectrometer, and this has been shown to be true not just for the \chem{H_2} energies back in 1964, but now also for several other molecules._x000d_ _x000d_ So are we at the stage where we can launch an array of calculations, each with just the atomic number changed in the input file, to reproduce the NIST energy level databases? Not quite. But I will show that for the 6e$^-$ molecule \chem{Li_2}, we have reproduced the vibrational spacings to within 0.001 cm$^{-1}$ of the experimental spectrum, and I will discuss present-day prospects for replacing laborious experiments for spectra of certain systems within the reach of today's ``computer spectrometers''._x000d_"

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/96957

DOI

https://doi.org/10.15278/isms.2017.MI08

Copyright and License Information

Copyright 2017 Nikesh S. Dattani

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