Partial deuterium substitution as a tool for identification of the most stable conformer of a polyatomic molecule. A case of the 2,5-bis(2-benzoxazolyl)-1,4-dimethoxybenzene in supersonic jet

2,5-bis(2-benzoxazolyl)-1,4-dimethoxybenzene (BBDB) and its symmetrically deuterated isotopomer (BBDB-d2) were studied in supersonic jets. The laser induced fluorescence excitation (LIF(E)) spectra of both compounds made possible the unequivocal identification of the spectral origins belonging to four isotopologues differing only in the orientation of the C–H/C–D bonds of the methyl groups with respect to the molecular plane. The splitting parameters of the origin (−1.1 cm−1, −0.35 cm−1, 0.3 cm−1) as well as the LIF(E) spectra of both isotopomers were satisfactorily reproduced by DFT and TD-DFT calculations.