A global view of isotopic effects on ro-vibrational spectra of six-atomic molecules: a case study of eleven ethylene species

Abstract

In this work, we present a global view of the impact of isotopic substitutions on the spectra of eleven ethylene isotopologues obtained from variational calculations using accurate ab initio potential energy and dipole moment surfaces. This may lead to some important changes in the molecular spectra due to symmetry breaking effects lowering the initial D_2h symmetry of ¹²C₂H₄ (¹²CH₂¹²CH₂) to C_2v, C_2h or C_s. For the very first time, we report ab initio predictions for ¹²C₂D₄ (¹²CD₂¹²CD₂) and three C_s species: ¹²CHD¹³CH₂, ¹³CHD¹²CH₂ and ¹²C₂HD₃ (¹²CD₂¹²CHD). To this end, we have considered the normal-mode approach based on our reduced Eckart-Watson Hamiltonian combined with ethylene ab initio surfaces. This work will contribute to the complete theoretical studies of the deuterated and ¹³C-enriched ethylene isotopologues. A total of 1252 vibrational levels are computed and all the corresponding transitions in the energy range of ≤3100 cm⁻¹ are predicted and compared to 151 bands assigned from experimental spectra analyses.