Leveraging MMW–MMW Double Resonance Spectroscopy to Understand the Pure Rotational Spectrum of Glycidaldehyde and 17 of Its Vibrationally Excited States

Broadband
measurements of glycidaldehyde in the frequency ranges
75–170 and 500–750 GHz were recorded to extend previous
analyses of its pure rotational spectrum in the microwave region.
The rotational parameters of the ground vibrational states for the
main isotopologue and the three singly 13C-substituted
isotopologues were considerably improved, and additional higher-order
parameters were determined. To identify new vibrationally excited
states in the dense and convoluted spectrum, an updated version of
the double-modulation double-resonance spectroscopy technique was
used. Connecting transitions with a shared energy level into series
and expanding these via Loomis–Wood plots proved to be a powerful
method, which allowed the identification of 11 new vibrationally excited
states in addition to the already known aldehyde torsions, v21 = 1 to v21 =
6. Interactions between several vibrational states were observed,
and three interacting systems were treated successfully. Rotational
transitions of glycidaldehyde were searched for in the imaging spectral
line survey ReMoCA obtained with the Atacama Large Millimeter/submillimeter
Array (ALMA) toward the high-mass star-forming region Sgr B2(N). The
observed spectra were modeled under the assumption of local thermodynamic
equilibrium (LTE). Glycidaldehyde, an oxirane derivative, was not
detected toward Sgr B2(N2b). The upper limit on its column density
implies that it is at least six times less abundant than oxirane in
this source.