Revealing the Structure and Noncovalent Interactions of Isolated Molecules by Laser-Desorption/Ionization-Loss Stimulated Raman Spectroscopy and Quantum Calculations

Abstract

The structural and dynamical characteristics of isolated molecules are essential, yet obtaining this information is difficult. We demonstrate laser-desorption jet-cooling/ionization-loss stimulated Raman spectroscopy to obtain Raman spectral signatures of nonvolatile molecules in the gas phase. The vibrational features of a test substance, the most abundant conformer of tryptamine, are compared and found to match those resulting from the scaled harmonic Raman spectrum obtained by density functional theory calculations. The vibrational signatures serve to identify the most prominent gauche conformer and evaluate its predicted electronic structure. These findings, together with noncovalent interaction (NCI) analysis, provide new insights into electron densities and reduced density gradients, assessing the hydrogen bonds (N–H···π and C–H···H–C) and interplay between attractive and repulsive NCIs affecting the structure. This approach accesses vibrational signatures of isolated nonvolatile molecules by tabletop lasers at uniform resolution and in a broad frequency range, promising great benefit to future studies.

Synergistic Spectroscopic and Computational Characterization Evidencing the Preservation or Flipping of the Hydroxyl Group of 2-Phenylethyl Alcohol upon Single and Double Hydration

“…Indeed, the specific class of neurotransmitters and neuromodulators, coupling between neighboring nerve cells and playing central roles in the human body, attracted considerable interest. Studies of these biomolecules, entailing the 2-phenylethylamine (PEA) building block, its hydrated cluster, − and other neutral, ,− and protonated compounds, − reveal diverse structural aspects. As these molecules comprise a flexible side chain and a rigid ring skeleton, where the former can adopt various configurations, forming alternative conformers is possible.…”

“…Accordingly, due to feature number inconsistency in the R2PI spectra and discrepancy in their assignment in previous studies, we are fascinated to reexamine the PEAL hydrates while utilizing the powerful ionization-loss stimulated Raman spectroscopy (ILSRS). ,,,,,− , This approach may reveal the O–H and C–H stretches and collective vibrational modes. We anticipate differences in the resulting ILRS spectral signatures, and their analysis will likely enable us to determine the structures of hydrated PEAL, even if they tolerate close energies.…”

Experimental/Computational Study on the Impact of Fluorine on the Structure and Noncovalent Interactions in the Monohydrated Cluster of ortho-Fluorinated 2-Phenylethylamine

“…Indeed, the investigation of different isolated neutral − and protonated NTs − and their hydrated clusters ,,− by various spectroscopic methods and quantum chemical calculations allowed us to obtain insight into electronic, vibrational, rotational, and energetic properties, conformational preferences, their potential energy surfaces (PESs), and scantly on the noncovalent interactions (NCIs). Specifically, the similarities between measured and calculated vibrational spectra enabled identification of the probed conformers existing in the molecular beam (MB).…”

Attaching Onto or Inserting Into an Intramolecular Hydrogen Bond: Exploring and Controlling a Chirality-Dependent Dilemma for Alcohols

“…In the present work, like in the methanol study [3], the main tool is FTIR jet spectroscopy, but important additional insights are obtained from Raman jet spectroscopy because cooperative hydrogen bonds may exhibit different intensity patterns for the hydride stretching fundamentals in these complementary techniques. Although conformationally selective stimulated Raman spectroscopy of selected (typically aromatic) non-volatile molecules is starting to become accessible [18,19], we explore the more general spontaneous Raman scattering variant [20], which also allows for limited volatility of the molecular ingredients.…”