Unveiling chiral optical constants of α-pinene and propylene oxide through ATR and VCD spectroscopy in the mid-infrared range

Sophisticated Attenuated Total Reflection Correction Within Seconds for Unpolarized Incident Light at 45°

“…To some degree, a loss function based on a two-trace two-dimensional correlation can provide a remedy. 20,25,26 A temperature controller is planned for future work.…”

“…As further examples and proofs, results are shown for octadecane (Figures S1-S3, Supplemental Material; octadecane is an unproblematic example) as well as for water on a different ATR accessory (FT-IR-2-ATR-2-Plate-1, Figures S4-S6, Supplemental Material) and a different crystal (FT-IR-1-ATR-1-Plate-2, Figures S7-S9, Supplemental Material and FT-IR-2-ATR-2-Plate-2, Figures S10-S12, Supplemental Material). We also provide comparisons between the formalism used in this work and the one used in Mayerhöfer et al 20 of the results for the optical constants functions for water and octadecane, Figures S13-S14 (Supplemental Material). The results show slight differences due to the fact that parts of the experimental spectra show slightly negative absorbance that was not corrected (the formalism used in Mayerhöfer et al 20 suppresses corresponding negative values for the absorption index function).…”

“…We also provide comparisons between the formalism used in this work and the one used in Mayerhöfer et al 20 of the results for the optical constants functions for water and octadecane, Figures S13-S14 (Supplemental Material). The results show slight differences due to the fact that parts of the experimental spectra show slightly negative absorbance that was not corrected (the formalism used in Mayerhöfer et al 20 suppresses corresponding negative values for the absorption index function). We verified for a synthetic sample that the results are identical when there are no negative ranges in the absorbance spectrum; see Figures S15-S16 (Supplemental Material).…”

“…Note that we explicitly take into account the wavenumber dependence of the refractive index of the incidence medium n 1 (ν) by using the refractive index function determined by Tatian. 19 Depending on the spectral resolution, the calculation requires about 2-10 s on a typical office PC, which means that it is much faster, up to two orders of magnitude, than an iterative correction procedure used, e.g., in Mayerhöfer et al 20 In contrast to the latter procedure, it usually also works when the condition of total reflection is violated around bands, i.e., when the refractive index of the sample becomes so large that the critical angle is larger than the AOI. For ZnSe and Diamond ATR crystals and an AOI of 45°this happens for refractive indices larger than about 1.7, which is quite often reached, e.g., for C=O or amide I bands.…”

Dielectric metasurface-assisted cavity ring-down spectroscopy for thin-film circular dichroism analysis

“…the difference in absorption, can be expressed as Δ A = ( ε R − ε L ) bC . 19 Here, ε R ( ε L ) represents the molar absorptivity of right (left) handed molecules. To enhance the sensitivity of the CD measurement, i.e.…”