Simulation of Vacuum UV Absorption and Electronic Circular Dichroism Spectra of Methyl Oxirane: The Role of Vibrational Effects

Abstract

Vibrationally resolved one-photon absorption and electronic circular dichroism spectra of (R)-methyl oxirane were calculated with different electronic and vibronic models selecting, through an analysis of the convergence of the results, the best compromise between reliability and computational cost. Linear-response TD-DFT/CAM-B3LYP/SNST electronic computations in conjunction with the simple vertical gradient vibronic model were chosen and employed for systematic comparison with the available experimental data. Remarkable agreement between simulated and experimental spectra was achieved for both one-photon absorption and circular dichroism concerning peak positions, relative intensities, and general spectral shapes considering the computational efficiency of the chosen theoretical approach. The significant improvement of the results with respect to smearing of vertical electronic transitions by phenomenological Gaussian functions and the possible inclusion of solvent effects by polarizable continuum models at a negligible additional cost paves the route toward the simulation and analysis of spectral shapes of complex molecular systems in their natural environment.

Aiming at an accurate prediction of vibrational and electronic spectra for medium‐to‐large molecules: An overview

“…While HT effects can be less important than in the case presented here, with the experimental band having a single sign, they can still modulate the shape and improve the overall agreement . The situation can become even more complex when multiple electronic states are involved since vibronic band‐shapes are very likely to overlap, canceling or enhancing each other, so that a proper representation of their envelope asymmetry is still necessary . Other studies based on chiral spectroscopies, including vibrational ones, can be found in references , , and .…”

“…It should be noted that, for spectra encompassing several electronic states, the band envelopes can vary strongly between transitions, with the overall band-shape made of their sum, which can lead to destructive effects in chiroptical spectroscopies, so the relative band-widths and intensities need to be correctly taken into account for a comparison with experiment. [28,[205][206][207] As a concluding remark, the AH spectra computed in Cartesian and internal coordinates are identical, validating the use of the simpler, Cartesian-based model for the electronic transitions of systems, which do not undergo large structural changes.…”

“…[16,67] The situation can become even more complex when multiple electronic states are involved since vibronic band-shapes are very likely to overlap, canceling or enhancing each other, so that a proper representation of their envelope asymmetry is still necessary. [16,206,207] Other studies based on chiral spectroscopies, including vibrational ones, can be found in references 29, 213, and 214.…”

Calculation of IR Spectra with a Fully Polarizable QM/MM Approach Based on Fluctuating Charges and Fluctuating Dipoles

“…MOXY is a widely exploited test system for computational models. [68][69][70][71][72][73][74] GLY, which bears an additional hydroxil group, has been previously studied both theoretically and experimentally. 36,54 In particular, it has been shown that eight different GLY conformers exist in aqueous solution, thus its theoretical modeling is challenging.…”

Chiroptical properties of 2,2’‐bioxirane

“…Moreover, methyloxirane has often been used as a model molecule in the development of VCD and OR theories. 3,[10][11][12][13][14][15] Indeed, the simplicity of its chemical structure is a major asset to perform sophisticated quantum calculations at the density functional theory (DFT) level in presence (explicit solvation model) or not of solvent molecules. 6,[16][17][18][19][20][21] Thus, large basis set can be used for DFT calculations allowing a prediction of its chiroptical properties with a high degree of accuracy.…”