Predicting odor from vibrational spectra: a data-driven approach.

This study investigates olfaction, a complex and not well-understood sensory modality. The chemical mechanism behind smell can be described by so far proposed two theories: vibrational and docking theories. The vibrational theory has been gaining acceptance lately but needs more extensive validation. To fill this gap for the first time, we, with the help of data-driven classification, clustering, and Explainable AI techniques, systematically analyze a large dataset of vibrational spectra (VS) of 3018 molecules obtained from the atomistic simulation. The study utlizes image representations of VS using Gramian Angular Fields and Markov Transition Fields, allowing computer vision techniques to be applied for better feature extraction and improved odor classification. Furthermore, we fuse the PCA-reduced fingerprint features with image features, which show additional improvement in classification results. We use two clustering methods, agglomerative hierarchical (AHC) and k-means, on dimensionality reduced (UMAP, MDS, t-SNE, and PCA) VS and image features, which shed further insight into the connections between molecular structure, VS, and odor. Additionally, we contrast our method with an earlier work that employed traditional machine learning on fingerprint features for the same dataset, and demonstrate that even with a representative subset of 3018 molecules, our deep learning model outperforms previous results. This comprehensive and systematic analysis highlights the potential of deep learning in furthering the field of olfactory research while confirming the vibrational theory of olfaction.

Effect of curve crossing induced dissociation on absorption and resonance Raman spectra: An analytically solvable model.

An analytically solvable model for the crossing of a harmonic and a Morse potential coupled by Dirac Delta function has been proposed. Further we explore the electronic absorption spectra and resonance Raman excitation profile using this model and found that curve crossing had significant effect on the resonance Raman excitation profile.

Barrierless electronic relaxation in solution: An analytically solvable model.

We propose an analytical method for understanding the problem of electronic relaxation in solution, modelled by a particle undergoing diffusive motion under the influence of two potentials. The coupling between the two potentials is assumed to be represented by a Dirac delta function. The diffusive motion in this paper is described by the Smoluchowski equation. Our solution requires the knowledge of the Laplace transform of the Green's function for the motion in both the uncoupled potentials. Our model is more general than all the earlier models, because we are the first one to consider the effect of ground state potential energy surface explicitly.

Effective Hamiltonian for chaotic coupled oscillators.

A generalized effective fitting Hamiltonian is tested against a model system of highly excited coupled Morse oscillators. At energies approaching dissociation, a very few resonance couplings in addition to the standard 1:1 and 2:2 couplings of the Darling-Dennison Hamiltonian suffice to fit the spectrum and match the large-scale features of the mixed regular and chaotic phase spaces, consisting of resonance zones organized around periodic orbits of low order that break the total polyad action.

The dynamics of solvation of an electron in the image potential state by a layer of polar adsorbates.

Recently, ultrafast two-photon photoemission has been used to study electron solvation at a two-dimensional metalpolar adsorbate interfaces [A. Miller et al., Science 297, 1163 (2002)]. The electron is bound to the surface by the image interaction. Earlier we have suggested a theoretical description of the states of the electron interacting with a two-dimensional layer of the polar adsorbate [K. L. Sebastian et al., J. Chem. Phys. 119, 10350 (2003)]. In this paper we have analyzed the dynamics of electron solvation, assuming a trial wave function for the electron and the solvent polarization and then using the Dirac-Frenkel variational method to determine it. The electron is initially photoexcited to a delocalized state, which has a finite but large size, and causes the polar molecules to reorient. This reorientation acts back on the electron and causes its wave function to shrink, which will cause further reorientation of the polar molecules, and the process continues until the electron gets self-trapped. For reasonable values for the parameters, we are able to obtain fair agreement with the experimental observations.