Authors: Cabezas, Carlos; Kawashima, Yoshiyuki; Bermudez, Celina; Usami, Tsuyoshi; Hirota, Eizi; Cernicharo, Jose


Publication date: 2023/04/15

DOI: 10.1016/j.saa.2023.122353

Abstract: A peptide linkage -(C–O)NH- containing molecule, N-ethylformamide, was investigated by rotational spec-troscopy in order to determine the molecular constants of its highest-energy conformer, cis -ac. Its rotational spectrum was observed in two different frequency ranges, in the 4-26 GHz frequency region using a Fourier transform microwave spectrometer and at millimeter wave frequencies between 75 and 116 GHz, employing a broadband high-resolution rotational spectrometer. The measurements at low frequencies allowed to resolve the hyperfine structure components due to nitrogen nuclear quadrupole coupling while the data at higher fre-quencies provided spectroscopic information about high order centrifugal effects. From a merged fit using all the observational data we have determined a total of thirteen molecular constants that provide a more accurate spectral modelling of the cis -ac conformer and serves a basis for their astronomical search. We have also observed spectra of five singly substituted isotopologues for the cis -ac conformer, three 13C and one for each of 15N and the deuterated species on the N-D position, from which we derived a partial r0 structure, in fair agreement with an ab initio result. In addition, the rotational transitions of the deuterated species of the most stable trans-sc conformer were observed and assigned and three rotational, five centrifugal distortion constants and nuclear quadrupole coupling constants of the nitrogen and deuterium nuclei were determined.