Raman spectroscopy of glycolic acid complexes with N 2 Jussi M.E. Ahokas a, * , Iwona Kosendiak b , Justyna Krupa b , Maria Wierzejewska b , Jan Lundell c a Department of Chemistry and Nanoscience Center, University of Jyv€ askyl€ a, P.O. Box 35, FI-40014, University of Jyv€ askyl€ a, Finland b Faculty of Chemistry, University of Wroclaw, F. Joliot-Curie 14, 50-383 Wroclaw, Poland c Department of Chemistry, University of Jyv€ askyl€ a, P.O. Box 35, FI-40014, University of Jyv€ askyl€ a, Finland article info Article history: Received 5 October 2018 Received in revised form 21 December 2018 Accepted 24 January 2019 Available online 25 January 2019 Keywords: Matrix isolation Raman spectroscopy High overtone excitation Isomerization Molecular complex abstract High overtone excitation induced conformational isomerization of glycolic acid e nitrogen complex in an argon matrix was investigated by Raman spectroscopy. The interaction between glycolic acid and ni- trogen change the green light (532 nm) induced isomerization processes compared to non-complexed glycolic acid. The 180  rotation around of the CeC bond and stabilization of carboxyl O]CeOeH dihe- dral 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 e nitrogen complex and the analysis of the isomeri- zation kinetics are presented. © 2019 Elsevier B.V. All rights reserved. 1. Introduction High overtone excitations are considered vibrational transitions where molecular vibrational modes are excited to high vibrational states on their ground electronic potential energy surface. An interesting focus area of high overtone excitations are the transi- tions where the OeH stretching modes are excited to states with a vibrational quantum number of 3e6. These transitions can be initiated by direct single photon absorption with photon energies ranging from near-infrared to visible light. Even though many at- mospheric reactions are initiated by electronic excitations of mol- ecules, the high overtone excitations with much weaker absorption cross-sections can play important role in atmospheric chemistry in certain conditions when high energy, i.e. ultraviolet, photons are lacking or the electronic states are not accessible [1 ,2]. The labo- ratory experiment can expand our understanding how the intra- molecular vibrational energy redistribution [3] takes place in molecules after high overtone excitation and what kind of chem- istry it may result to. Glycolic acid, a smallest a-hydroxy acid, is a good prototype molecule to investigate high overtone induced chemistry of small organic molecules. Two functional OH groups, alcohol and carboxyl, provide two different channels to access high overtone states of the OeH stretching vibrations in the molecule. Moreover, the high overtone transitions of the OeH stretching vibrations typically possess larger cross-section than the CeH, SeH, and NeH stretching vibrations [4e6]. Thus, the high overtone excitations are more easily accessible for the OeH stretching modes. The vibra- tional fundamental and the first overtone excitation induced isomerization of glycolic acid has been investigated in argon and nitrogen matrices [7e9]. Three different structural conformers of glycolic acid has been found to be stable in an argon matrix after near-infrared excitation induced isomerization reactions, and the fourth conformer have only been found in a nitrogen matrix, where the first overtone excitation yields completely different products than in an argon matrix [9]. The experimentally observed con- formers and their observed overtone excitation induced reaction paths are shown in Fig. 1 . Recently, we have shown that the high overtone induced isomerization of glycolic acid in an argon matrix [10] follows different pathways than the isomerization initiated by the first overtone excitations [9]. The same isomerization products can be obtained in an argon matrix by both excitation approaches, but near-infrared excitation yields completely different isomerization reactions in a nitrogen matrix [9, 10]. The appearance of the SST conformer only in a nitrogen matrix [9] has been proposed to * Corresponding author. E-mail address: jussi.m.e.ahokas@jyu.fi (J.M.E. Ahokas). Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc https://doi.org/10.1016/j.molstruc.2019.01.080 0022-2860/© 2019 Elsevier B.V. All rights reserved. Journal of Molecular Structure 1183 (2019) 367e372