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The photochemistry of matrix-isolated glycolic acid, induced by UV light, was studied by FTIR spectroscopy and B3LYPD3/6-311++G(3df,3pd) calculations. Several decomposition pathways were found to take place upon 212 nm and 226 nm wavelengths irradiation. A number of complexes formed between photoproducts were identified, among them those of formaldehyde with water, carbon monoxide and carbon dioxide as well as the H2O-CO complexes. The structure and spectroscopic assignment of the photoproducts were made comparing the experimental results with the theoretical predictions and available literature data. The observed formation of different complexes indicates various pathways for their formation resulting from UV-induced photodecomposition of different precursor isomers. peerReviewed

Conformational changes of the monomeric safrole (5-(2-propenyl)-1,3-benzodioxole) isolated in low temperature xenon matrices were induced thermally or using narrow-band UV radiation. The rotation of the allyl group taking place in the studied matrices was followed by FTIR spectroscopy. Safrole represents a challenging example of a flexible molecule highlighting the importance of dispersion interactions and anharmonic effects in the structural, spectroscopic and energetic analysis. Structures of the safrole conformers, their energetics and infrared spectra have been calculated using various computational methods ranging from density functional theory (DFT) to coupled cluster (CC). The best theoretical results were obtained by integrating CCSD(T) energies including complete basis set extrapolation and core-valence corrections with B2PLYP-D3 equilibrium structures and hybrid B2PLYP-D3/B3LYP-D3 anharmonic computations for IR spectra and thermodynamics.

A matrix isolation study of structure and infrared spectra of o-guaiacol (o-methoxyphenol, GU) has been performed showing that the most stable conformer of the compound is present in argon and xenon matrices. Photochemical reactions of o-guaiacol were induced using UV-laser radiation and followed by the FTIR spectroscopy. Four photolysis pathways have been considered based on the positions of new bands appearing during irradiation of the matrices. It was concluded that the cleavage of the O H bond is an initial step of the reactions and a number of photoproducts have been identified originating from the subsequent ring opening and decarbonylation processes as well as the O CH3 bond cleavage. Among the photoproducts are cyclopetadienone and long-chain ketenes with conjugated/cumulated C O and C C bonds.

Glycolic acid (GA) dimers were studied in low temperature argon matrices by means of FTIR spectroscopy. Experimentally, the dimers were produced when monomeric glycolic acid molecules were thermally mobilized upon annealing of argon matrices at 25–35 K. The experimental spectra observed upon annealing indicate the presence of three different dimer structures. Computationally, MP2 and DFT calculations were used to study the potential dimer species in order to scrutinize the possible dimer structures, their energetics and their spectral features. Altogether 27 local minima were found for dimer structures for the three lowest conformers of glycolic acid considered based on previous studies on glycolic monomer in argon matrices. Comparing the computational and the experimental spectra especially in the O–H and C=O stretching regions it was possible to assign the experimental observations to the three most stable dimer species. peerReviewed

Matrix isolation FTIR spectroscopy has been combined with quantum chemical calculations in the aim to characterize complexes of isothiocyanic acid HNCS with SO2. The geometries of the 1:1, 1:2 and 2:1 complexes were optimized at the MP2 and DFT (B3LYPD3) levels of theory with the 6-311++G(3df,3pd) basis set. Five different HNCS⋯SO2 structures of the 1:1 stoichiometry were optimized. Three of them involve a weak NH⋯O hydrogen bond whereas two other geometries are stabilized by van der Waals interactions of various types. The HNCS/SO2/Ar spectra analysis evidences that at least one of the three hydrogen bonded structure is present after deposition of the matrices whereas the most stable van der Waals HNCS⋯SO2 structure as well as complexes of the 1:2 stoichiometry were detected upon annealing.

UV photochemistry of H 2 O 2 isolated in solid nitrogen at 15 K has been studied experimentally by FTIR matrix isolation technique and theoretically using DFT and MP2 methods. The major photoproducts were identified as (i) nitrous oxide and N 2 O⋯H 2 O complex and (ii) free and complexed to N 2 O hydroxyl radicals. Except for the OH radicals all observed species are unique and characteristic for H 2 O 2 photolysis in solid nitrogen. The identities of the products have been confirmed by comparison with results of quantum chemical calculations, and reference to the spectral data of related molecules. Differences in the photolysis course upon irradiation at 230 and 212 nm are discussed.

A quantum mechanical study of the potential energy surface for the HNCS dimer is reported. The calculations were performed using DFT and ab initio MP2 methods. The most stable is a cyclic form with a double N–H⋯S interaction and the interaction energy in the range of 16.91–18.92 kJ mol−1. An open HNCS dimer bound by the N–H⋯N hydrogen bond is by ca 3.3–5.1 kJ mol−1 less stable. Experimental FTIR matrix isolation studies of HNCS/N2 system show that exclusively less stable open dimer is formed in solid nitrogen. Possible reasons for the observed discrepancy between theory and experiment are discussed.

The title compound 1,2,4-triazolyl-3-carboxylic acid (TC) belongs to the rarely studied N–H azoles bearing a carboxylic group attached directly to the ring. Thermal decomposition of TC was studied in detail both experimentally using FTIR matrix isolation technique and theoretically at the B3LYPD3 and B3LYP levels with 6–311++G(2d,2p) basis set. Both concerted and stepwise pathways were considered theoretically for unimolecular decarboxylation of TC. Experimentally, in addition to the 1,2,4-triazole (TR) and carbon dioxide, two weak molecular complexes formed between TR and CO2 were detected in the studied matrices. Based on a comparison of the predicted and observed wavenumber shifts, the structures of the complexes have been confirmed.

High overtone excitation induced conformational isomerization of glycolic acid – nitrogen complex in an argon matrix was investigated by Raman spectroscopy. The interaction between glycolic acid and nitrogen change the green light (532 nm) induced isomerization processes compared to non-complexed glycolic acid. The 180° rotation around of the Csingle bondC bond and stabilization of carboxyl Odouble bondCsingle bondOsingle bondH dihedral angle to trans position were the main conformational changes observed in the complex of the lowest energy conformer and nitrogen. Interestingly, only one stable light-induced conformational product was observed, which isomerises back to the lowest energy conformer upon prolonged irradiation at 532 nm. The vibrational Raman spectrum of glycolic acid – nitrogen complex and the analysis of the isomerization kinetics are presented. peerReviewed

The interaction of weakly bonded complexes of atmospheric constituents with the electromagnetic spectrum available in Earth’s atmosphere can induce direct excitation to electronic excited states as well as the excitation of higher vibrational states (overtones) of the electronic ground state. A better understanding of these phenomena requires improved theoretical support by including the anharmonic and vibro-electronic effects on both the band positions and transition intensities. In this work, generalized second-order vibrational perturbation and time-independent Franck–Condon and Herzberg–Teller computations are exploited together with a density functional theory (DFT)/coupled cluster (CC) scheme and its extension to the excited electronic states. Structural and spectroscopic properties are calculated for isolated formaldehyde and its complexes with H2O, CO, SO2 and H2O2, focusing on how small molecules may affect the interactions with NIR to UV irradiation.

In situ photochemical transformations of monomers of 2-methoxy-4-(prop-1-enyl)phenol (isoeugenol) and 2-methoxy-4-(prop-2-enyl)phenol (eugenol) isolated in low temperature matrices were induced by tunable UV laser light, and the progress of the reactions was followed by FTIR spectroscopy. Conformer-selective E ↔ Z geometrical isomerizations could be successfully induced by irradiation at different wavelengths from the 310–298 nm range in the isoeugenol molecule, contains an asymmetrically substituted exocyclic C═C bond. Photolysis of both studied compounds was also observed, with H-atom shift from the OH group and formation of two types of long-chain conjugated ketenes. The photoproduced ketenes were found to undergo subsequent photodecarbonylation. Interpretation of the observed photoprocesses was supported by quantum chemical calculations undertaken at different levels of theory (DFT, MP2, QCISD).