Deconstructing Vibrational Motions on the Potential Energy Surfaces of Hydrogen-Bonded Complexes

Abstract

Internal vibrations underlie transient structure formation, spectroscopy, and dynamics. However, at least two challenges exist when aiming to elucidate the contributions of vibrational motions on the potential energy surfaces. One is the acquisition of well-resolved experimental infrared spectra, and the other is the development of efficient theoretical methodologies that reliably predict band positions, relative intensities, and substructures. Here, we report size-specific infrared spectra of ammonia clusters to address these two challenges. Unprecedented agreement between experiment and state-of-the-art quantum simulations reveals that the vibrational spectra are mainly contributed by proton-donor ammonia. A striking Fermi resonance observed at approximately 3210 and 3250 cm −1 originates from the coupling of NH symmetric stretch fundamentals with overtones of free and hydrogen-bonded NH bending, respectively. These novel, intriguing findings contribute to a better understanding of vibrational motions in a large variety of hydrogen-bonded complexes with orders of magnitude improvements in spectral resolution, efficiency, and specificity.

Disentangling the Complex Vibrational Spectra of Hydrogen-Bonded Clusters of 2-Pyridone with Ab Initio Structural Search and Anharmonic Analysis

“…In the spectrum of 2PY-(MeOH), two peaks at 3335 and 3189 cm The vibrational features of 2PY-(NH 3 ) between 3200 and 3400 cm −1 were attributed to ammonia by Leutwyler and coworkers. Indeed, the three main groups at 3230, 3300, and 3400 cm −1 resemble the vibrational pattern of NH 3 in ammonia clusters 33,34 and ammonia-pyridine clusters. 7 The Fermi resonance pattern of hydrogen-bonded NH 3 was analyzed previously in which the two asymmetric NH stretching fundamentals were often found to be at and above 3400 cm −1 .…”

Rapid Multialkylation of Aqueous Ammonia with Alcohols by Heterogeneous Iridium Catalyst under Simple Conditions

“…As ammonia gas (0.1 vol. % in He) was insufflated, NH 3 symmetric bending (930 and 965 cm −1 ) [49] and symmetric stretch of NH in proton‐acceptor ammonia (3333 cm −1 ) [50] can be observed distinctly and increase cumulatively. The decreasing of O−H bending in benzyl alcohol (1209 cm −1 ) [51,52] shows the conversion of benzyl alcohol.…”

Infrared–vacuum ultraviolet spectroscopy of the CH stretching vibrations of jet‐cooled aromatic azine molecules and the anharmonic analysis

“…Kuo and coworkers succeeded in analyzing F-R of the X H stretching vibration by using ab initio anharmonic algorithms using reduced-dimensional potential energy surfaces (PESs) up to CCSD(T)/aug-cc-pVTZ level of theory. [7,[13][14][15][16][17][18][19] It is well known that many of the IR spectra in the C H stretching region of aromatic molecules show very complicated features due to F-R. For example, benzene exhibits three absorption bands in the 3,020-3,130 cm À1 region due to F-R between an IR active C H stretching vibration (ν 20 ) and the combination bands of C H bending vibrations. [20,21] For the mono-substituted benzene, toluene exhibits more than nine bands [22] in the aromatic C H stretching vibration region, and phenol exhibits more than 15 bands in the C H stretching region.…”