Laboratory Characterization and Interstellar Search for a New Interstellar Candidate: 2,3-Butadienal

Three aldehydes with
unsaturated substituents: propenal,
3-hydroxypropenal,
and propynal, have been detected in the interstellar medium (ISM).
The structurally related molecule 2,3-butadienal, an aldehyde with
an allenyl substituent, therefore represents a compelling new target
for interstellar searches. To date, however, no laboratory measurements
of its rotational spectrum have been reported. Here, we present the
first measurements and analysis of the rotational spectrum of the
most stable trans-2,3-butadienal in the 150–485 GHz frequency
range, with the aim of providing the accurate spectroscopic predictions
required for astronomical observations. Guided by quantum chemical
calculations, we assign the ground state and the two lowest excited
vibrational states and analyze the latter within a Coriolis-coupled
framework. The resulting high-precision spectroscopic parameters enable
reliable frequency predictions over a broad range of quantum numbers.
Using this new spectroscopic model, we searched for 2,3-butadienal
in public astronomical data toward TMC-1, Sgr B2(N), and G +0.693–0.027.
No transitions of this molecule were detected in any of these sources.
Upper limits to its column density were therefore derived, and the
implications for its possible formation pathways in the ISM are discussed.
The comprehensive spectroscopic characterization reported here provides
a robust foundation for future astronomical searches and will facilitate
efforts to detect 2,3-butadienal in diverse interstellar environments.