Pushing measurements and interpretation of VCD spectra in the IR, NIR and visible ranges to the detectability and computational complexity limits

Year: 2024

Authors: Fuse M., Mazzeo G., Bloino J., Longhi G., Abbate S.

Autors Affiliation: Univ Brescia, Dipartimento Med Mol & Traslazionale, Viale Europa 11, I-25123 Brescia, Italy; Scuola Normale Super Pisa, Piazza Cavalieri, I-56125 Pisa, Italy; CNR, Ist Nazl Ott INO, Res Unit Brescia, CSMT, VIA Branze 45, I-25123 Brescia, Italy.

Abstract: (R)-Limonene VCD and IR absorption spectra for neat liquid samples are considered from 900 to 16,000 cm(-1), using mostly data by Nafie et al. up to 10,000 cm(-1) and from previous investigations of the Brescia group. New VCD data are recorded in the merely overtone and combination region between 1800 and 2400 cm(-1) and for the Delta n = 6 overtone CH-stretching region above 15,000 cm(-1). The GVPT2 anharmonic DFT calculations permit satisfactory interpretation of the fundamental + overtone/combination of deformation modes in the mid-IR up to 3500 cm(-1). The GVPT2 approach is also used for the first CH-stretching overtone regions together with their combination with deformation modes up to 9000 cm(-1). Then the local-mode approach developed within the DFT protocol is employed in all the CH-stretching regions (fundamental + overtones) and is found to satisfactorily account for the observed spectra, justifying the constant VCD pattern observed for all overtones. On the basis of the local-mode model the components of the bisignate VCD spectrum are attributed to the stretchings of the axial and equatorial CH bonds in alpha-position with respect to the ring CC double bond.

Journal/Review: SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY

Volume: 305      Pages from: 123496-1  to: 123496-10

More Information: The authors thank David A. Lightner of University of Nevada, Reno for helpful discussions, for encouraging VCD research in the NIR region and for providing us the 19-cm cuvette used for the VCD measurements in the 700-600 nm region. Funding was provided by the Italian Ministry of University and Research (MUR) through the PRIN program (PRIN 2017, project Physico-chemical Heuristic Approaches: Nanoscale Theory of Molecular Spec-troscopy (PHANTOMS) , prot. 2017A4XRCA and PRIN 2020, project Photoreactive Systems upon Irradiation: Modelling and Observation of Vibrational Interactions with the Environment’’ (PSI-MOVIE) , prot. 2020HTSXMA) . The CINECA award under the ISCRA (IsC97_CSoVCS) initiative is acknowledged for providing high-performance computing facilities. Computing facilities from SNS HPC are also acknowledged.
KeyWords: Vibrational Circular Dichroism (VCD); Near Infrared (NIR); Anharmonicity; Generalized Vibrational Perturbative Theory at the Second Order (GVPT2); Local-mode approach; Limonene
DOI: 10.1016/j.saa.2023.123496

Citations: 4
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