Sum-frequency vibrational spectroscopy of limonene chiral liquids due to the nonadiabatic effect

Abstract

Using quantum computations we study sum-frequency vibrational spectroscopy of limonene chiral liquids due to the nonadiabatic effect in the non-resonant case for the first time. The nonadiabatic effect has an important impact on non-resonant antisymmetric polarizability and chiral sum-frequency vibrational spectroscopy. The theoretical spectroscopy agrees with the experimental spectroscopy. However, the nonadiabatic effect only has a small influence on non-resonant Raman. Bulk sum-frequency vibrational spectroscopy may become a powerful method of investigating the nonadiabatic effect and the nonradiative transition between excited electronic states for chiral molecules.

Chirality discrimination at the carvone air/liquid interfaces detected by heterodyne-detected sum frequency generation

“…We have demonstrated the ability of HD-SFG to directly probe the chirality at interfaces even without the electronic-resonance. The three strong vibrational peaks can be assigned to symmetric CH 2 (2821 cm −1 ), symmetric CH 3 (2873 cm −1 ) and single CH (2910 cm −1 ) stretching modes respectively [8,35]. The weak vibrational peak at 2957 cm −1 likely belongs to the asymmetric CH 2 or CH 3 stretching mode, because it has the opposite sign to the symmetric stretching peaks at 2821 cm −1 and 2873 cm −1 .…”

Herzberg–Teller Effect Predominates in Sum-Frequency Vibrational Spectroscopy of Limonene Chiral Liquids

“…They found that the antisymmetric vibrational Raman polarizability is much weaker than the symmetric one in a nonresonant case . In 2018, using quantum chemistry computations, we calculated the antisymmetric nonresonant Raman polarizability and the bulk SFVS off-electronic resonance for limonene chiral liquids, and we found that when the nonadiabatic terms between the different excited electronic states are taken into consideration, the intensities of the computational chiral SFVS are much smaller than those of the experimental spectra . We are curious about the reason why the spectral intensities we calculated are small.…”

“…In the nonresonant case, the sum-frequency light ω is not resonant with molecular excited electronic states and μ k is the k ( k = x , y , z ) component of the electric dipole operator. The anti-Stokes Raman tensor M ij is written as , where n is the excited electronic state, δ is the corresponding vibrational state, ω ( n ,δ)( g , v ) ( v = 0, 1) is the energy difference between the excited vibronic state | n ,δ⟩ and the ground vibronic state | g , v ⟩, and Γ ( n ,δ)( g , v ) is the corresponding damping constant. M ij can be written as the sum of A and B terms The A term is from the electric dipole contribution, and the B term is due to the nonadiabatic effect.…”

“…We are curious about the reason why the spectral intensities we calculated are small. Note that the shifts of the potential energy minimum between the ground and the excited electronic states along the normal modes are assumed to be very small and taken as zero in our computations …”

Time-Variable Chiroptical Vibrational Sum-Frequency Generation Spectroscopy of Chiral Chemical Solution

“…However, it was not possible to accurately determine how many bands contribute to the observed chiral spectrum, because a complicated spectral overlap between positive- and negative-signed chiral peaks, which in part cancel out one another, makes it challenging to fit the data unambiguously. Other FT-IR, Raman, and VCD studies have reported that three or more vibrational modes could contribute to the corresponding C–H stretch vibrational spectra of chiral limonene liquid. ,− A more reliable and accurate determination method for the spectroscopic parameters has thus been needed. We here perform global fitting analyses of multiple sets of time-delayed VSFG spectra to determine the spectroscopic parameters of R -(+)-limonene.…”