The first step to
shed light on the abiotic synthesis of biochemical
building blocks, and their further evolution toward biological systems,
is the detection of the relevant species in astronomical environments,
including earthlike planets. To this end, the species of interest
need to be accurately characterized from structural, energetic, and
spectroscopic viewpoints. This task is particularly challenging when
dealing with flexible systems, whose spectroscopic signature is ruled
by the interplay of small- and large-amplitude motions (SAMs and LAMs,
respectively) and is further tuned by the conformational equilibrium.
In such instances, quantum chemical (QC) calculations represent an
invaluable tool for assisting the interpretation of laboratory measurements
or even observations. In the present work, the role of QC results
is illustrated with reference to glycolic acid (CH
2
OHCOOH),
a molecule involved in photosynthesis and plant respiration and a
precursor of oxalate in humans, which has been detected in the Murchison
meteorite but not yet in the interstellar medium or in planetary atmospheres.
In particular, the equilibrium structure of the lowest-energy conformer
is derived by employing the so-called semiexperimental approach. Then,
accurate yet cost-effective QC calculations relying on composite post-Hartree–Fock
schemes and hybrid coupled-cluster/density functional theory approaches
are used to predict the structural and ro-vibrational spectroscopic
properties of the different conformers within the framework of the
second-order vibrational perturbation theory. A purposely tailored
discrete variable representation anharmonic approach is used to treat
the LAMs related to internal rotations. The computed spectroscopic
data, particularly those in the infrared region, complement the available
experimental investigations, thus enhancing the possibility of an
astronomical detection of this molecule.