0.06 cm−1 discrepancy for Li2→ 2Li and 0.994 cm−1 for C → C+ between laboratory and computer spectrometers

Dattani, Nikesh S.

Permalink

https://hdl.handle.net/2142/100779 Copy

Description

Title

0.06 cm−1 discrepancy for Li2→ 2Li and 0.994 cm−1 for C → C+ between laboratory and computer spectrometers

Author(s)

Dattani, Nikesh S.

Issue Date

2018-06-20

Keyword(s)

Mini-symposium: New Ways of Understanding Molecular Spectra

Abstract

The energy at the empirical bond length of Li2(13Σ + u ) of 4.1700A˚ b was obtained at all-electron FCI level with an augcc-pCV5Z-NR basis set, all-electron CCSDT(Q) with aug-cc-pCV7Z-NR, and all-electron CCSD(T) with aug-cc-pCV8ZNR; along with corrections due to special relativity converged with respect to electron correlation and basis set size using the spin-free Dirac-Coulomb Hamiltonian, and further such corrections at the Hartree-Fock level using the Breit and Gaunt Hamiltonians. Corrections to the point-size nucleus approximation were calculated but found to be negligible. The result was compared to the lowest energy of the best empirical potentialsb with the empirical Born-Oppenheimer breakdown corrections removed, making it essentially an infinite-mass to infinite-mass comparison. The discrepancy between the energy obtained from laboratory spectroscopy and the energy obtained completely by the computer was only 0.06 cm−1 , which is of the same order of magnitude as the uncertainty on the empirical value, which is ±0.007 cm−1 before including the added uncertainty coming from the Born-Oppenheimer breakdown parameter u0 which itself has an uncertainty of 0.01 cm−1 . It is discussed what is necessary for the computer spectrometer to outperform the laboratory spectrometer. The ionization energy of the carbon atom was calculated at all-electron FCI level with aug-cc-pCV8Z-NR and aug-ccpCV7Z-NR basis sets (the latter only for basis set extrapolation); along with corrections due to special relativity converged with respect to electron correlation and basis set size using the 1e − X2C Hamiltonian, further corrections using stateaveraged Dirac-Fock for the contribution from the Breit Hamiltonian and some QED contributions; along with DBOC corrections to the clamped nucleus approximation converged with respect to electron correlation and basis set size. Again, corrections to the point-size nucleus approximation were calcualted but found to be negligible. The final energy was compared to the very recent experimental value published by NISTc with the experimental spin-orbit lowering of 12.672508 cm−1 removed. The discrepancy was 0.994 cm−1 compared to the ±0.009 cm−1 uncertainty in the laboratory value.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/100779

DOI

10.15278/isms.2018.WB08

Copyright and License Information

Copyright 2018 Nikesh S. Dattani

Owning Collections