Nuclear Quadrupole Hyperfine Structure in HC14N/H14NC and DC15N/D15NC Isomerization: A Diagnostic Tool for Characterizing Vibrational Localization

TL;DR

This study shows that nuclear quadrupole hyperfine interactions can serve as a sensitive diagnostic tool to identify vibrational localization during isomerization in specific nitrogen-containing molecules, using high-level ab initio calculations.

Contribution

It introduces the use of nuclear quadrupole hyperfine interactions as a diagnostic marker for vibrational localization along the isomerization pathway, supported by ab initio calculations and experimental agreement.

Findings

Hyperfine interactions are highly sensitive to chemical bonding changes.

Hyperfine structure can determine the potential well localization of vibrational states.

Excellent agreement between calculations and measurements validates the diagnostic approach.

Abstract

Large-amplitude molecular motions which occur during isomerization can cause significant changes in electronic structure. These variations in electronic properties can be used to identify vibrationally-excited eigenstates which are localized along the potential energy surface. This work demonstrates that nuclear quadrupole hyperfine interactions can be used as a diagnostic marker of progress along the isomerization path in both the HC14N/H14NC and DC15N/D15NC chemical systems. Ab initio calculations at the CCSD(T)/cc-pCVQZ level indicate that the hyperfine interaction is extremely sensitive to the chemical bonding of the quadrupolar 14N nucleus and can therefore be used to determine in which potential well the vibrational wavefunction is localized. A natural bonding orbital analysis along the isomerization path further demonstrates that hyperfine interactions arise from the asphericity of the electron density at the quadrupolar nucleus. Using the CCSD(T) potential surface, the quadrupole coupling constants of highly-excited vibrational states are computed from a one-dimensional internal coordinate path Hamiltonian. The excellent agreement between ab initio calculations and recent measurements demonstrates that nuclear quadrupole hyperfine structure can be used as a diagnostic tool for characterizing localized HCN and HNC vibrational states.