Accurate Quantum Chemical Spectroscopic Characterization of Glycolic Acid: A Route Toward its Astrophysical Detection

Abstract

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.

In Vitro and In Silico Vibrational–Rotational Spectroscopic Characterization of the Next-Generation Refrigerant HFO-1123

“…According to the available literature, the adopted hybrid force field is expected to predict fundamental transition frequencies with an average accuracy within 5 cm –1 , a maximum error of 10 cm –1 , and anharmonic IR intensities with an error of a few km mol –1 ; hence, ChS:rDSD simulations have been used to guide and support the analysis of the observed spectra. 30 , 36 , 38 , 64 , 65 …”

“…The spectroscopic parameters relevant for rotational spectroscopy, specifically equilibrium and ground state rotational constants as well as quartic centrifugal distortion terms, are summarized in Table , where theoretical predictions are compared against the experimental data in the I r representation of the Watson’s A reduced Hamiltonian . A well consolidated procedure was followed, ,, and the best estimates of ground state rotational constants have been obtained by augmenting those of the equilibrium configuration computed according to the CCSD­(T)/CBS+CV composite scheme through rev-DSDPBEP86-D3/jun-cc-pVTZ vibrational corrections. The resulting parameters are in very good agreement with the corresponding experimental counterparts with discrepancies of 0.06%, thus confirming the accuracy of the CCSD­(T)/CBS+CV equilibrium geometry as well as the reliability of the rev-DSDPBEP86 vibrational contributions.…”

“…This has harmonic frequencies estimated by the ChS method mixed with cubic and semidiagonal quartic force constants evaluated at the rev-DSDPBEP86-D3 level, while hybrid anharmonic intensities have been obtained from ChS and rev-DSDPBEP86-D3 contributions, according to eq . According to the available literature, the adopted hybrid force field is expected to predict fundamental transition frequencies with an average accuracy within 5 cm –1 , a maximum error of 10 cm –1 , and anharmonic IR intensities with an error of a few km mol –1 ; hence, ChS:rDSD simulations have been used to guide and support the analysis of the observed spectra. ,,,, …”

“…On their own, vibrational investigations are ever increasingly supported by quantum chemical (QC) calculations that work as a guide and a support for the assignment of the experimental signals. In fact, reliable predictions of vibrational transition frequencies and IR intensities can be obtained beyond the rigid-rotor-harmonic-oscillator model without the need of any empirical scaling factor and with a full account of anharmonic resonances with accuracies within 10 cm –1 for fundamental frequencies and a few km mol –1 for IR intensities. , Concerning halocarbons, it has been demonstrated that such accuracy can be reached using the coupled cluster theory with singles, doubles, and a perturbative estimate of the triples, CCSD­(T), , coupled to large basis sets. − An alternative and more cost-effective approach is represented by QM/QM' computational protocols involving CCSD­(T)-based composite schemes for geometry and harmonic properties, coupled with anharmonic effects described through density functional theory (DFT). , …”

Fast exploration of potential energy surfaces with a joint venture of quantum chemistry, evolutionary algorithms and unsupervised learning

“…In particular, we are concerned with the use of metaheuristics in the exploration of the Potential Energy Surfaces (PESs) of flexible molecular systems of medium size (roughly containing less than 100 atoms). In previous contributions [15][16][17] we have proposed and validated the application of one of such algorithms, namely the (λ + µ) Island Model Evolutionary Algorithm (IM-EA hereafter), to the investigation of the conformational landscape of biomolecule building blocks 18 or relatively simple organometallic systems 19 . The present contribu-tion presents a number of relevant improvements to the IM-EA method: (i) in the previous contribution we simply checked the capabilities of the method in exploring PESs of flexible systems with the goal of completeness without an in depth discussion of the importance of various components in the method, which is presented in this manuscript; (ii) we previously limited the exploration to dihedral angles of isolated flexible systems, whereas here we present also a new set of operators based on quaternions 20,21 able to deal with inter-molecular interactions; (iii) we add a number of improvements to the method, with new mutation operators and the Hall of Fame mechanism (see section 2.1) and (iv) introduce effective unsupervised clustering of candidate structures in order to reduce as much as possible the number of expensive quantum chemical (QC) computations; neither the computer code, nor the case studies discussed below were presented before.…”