Global view on isotopic effects in ro-vibrational spectra of six-atomic molecules: case study of eleven ethylene species

In this work, we present a global view of the impact of isotopic substitutions on eleven ethylene isotopologues spectra obtained from variational calculations using accurate {\it ab initio} potential energy and dipole moment surfaces. That may lead to some important changes in molecular spectra due to symmetry breaking effects lowering the initial D_{2h} symmetry of ^{12}$C_2H_4 ( \equiv ^{12}CH_2^{12}CH_2) to C_{2v}, C_{2h} or C_s. For the very first time, we report {\it ab initio} predictions for ^{12}C_2D_4 (\equiv ^{12}CD_2^{12}CD_2) and three C_s species :^{12}CHD^{13}CH_2, ^{13}CHD^{12}CH_2 and ^{12}C_2HD_3 (\equiv ^{12}CD_2^{12}CHD). To this end, we have considered the normal-mode approach based on our reduced Eckart-Watson Hamiltonian combined with ethylene {\it ab initio} surfaces. This work will contribute to the complete theoretical studies of the deuterated and ^{13}C-enriched ethylene isotopologues. A total of 1252 vibrational levels is computed and all the corresponding transitions in the energy range \leq 3100 cm^{-1} are predicted and compared to 151 bands assigned from experimental spectra analyses.