Computational molecular spectroscopy

Abstract

Molecular spectroscopy techniques are unique tools to probe molecular systems non-invasively and investigate their structure, properties, and dynamics in different environments and physicochemical conditions. Different spectroscopic techniques and their combination can lead to a more comprehensive picture of investigated systems. However, the increasing sophistication of these experimental techniques makes it more and more complex and difficult to interpret the results without the help of computational chemistry. As a consequence, computational molecular spectroscopy has progressively changed from a highly specialized field to a general tool also employed by experimentally-oriented researchers. Computational spectroscopy, born as a branch of quantum chemistry for providing predictions of spectroscopic properties and features, evolved as an independent field. In this Primer, we focus on the characterization of medium-sized molecular systems by means of different spectroscopic techniques. We first provide essential information about the characteristics, accuracy and limitations of the available computational approaches, and select examples with the aim of illustrating general trends, that is outcomes of general validity that can be used for modeling spectroscopic phenomena. We emphasize the need for estimating error bars and limitations, coupling accuracy with interpretability, and discuss the results in terms of widely recognized chemical concepts.

Ab Initio Study of Fine and Hyperfine Interactions in Triplet POH

“…The chemical composition of the ISM is mainly investigated via the recognition of rotational or vibrational transitions in the spectra observed by ground-based radio telescopes and/or spaceborne facilities [ 13 ]. The rotational spectrum is often denoted as a collection of “molecular fingerprints” because it substantially depends on the atomic composition and on the molecular structure [ 14 , 15 , 16 , 17 ]. In fact, both PN and PO, as well as about 93% of the molecules detected in Space (see for a comprehensive list.…”

“…State-of-the-art spectrometers, working in the millimetre/submillimetre-wave regions, possess a resolving power that allows, in many cases, identifying and resolving such hyperfine structures [ 23 , 24 ]. On the other hand, the line-by-line assignment of these complex patterns greatly benefits from the availability of effective theoretical simulations based on accurate quantum-chemical techniques [ 14 , 15 , 17 , 25 ]. In fact, even though computational spectral predictions are always affected by uncertainties in the absolute line position, the hyperfine structures can be reproduced with great accuracy once the critical spectroscopic parameters are computed at a suitable level of theory [ 14 , 25 , 26 ].…”

Anharmonic DFT Study of Near-Infrared Spectra of Caffeine: Vibrational Analysis of the Second Overtones and Ternary Combinations

“…In contrast, the analogous information available for NIR spectroscopy remains fairly shallow [23]. Because of the anharmonicity, it is difficult to yield an exhaustive interpretation of NIR spectra by means of classical methods [24]. In recent years, significant progress in theoretical methods of calculation of anharmonic spectra was observed [25][26][27].…”

Theoretical Simulation of Near-Infrared Spectrum of Piperine: Insight into Band Origins and the Features of Regression Models

“…17,31 Several other examples of accurate calculation of overtones and combination bands that can also be observed as weak bands in IR spectra, together with the anharmonic effects that affect fundamental bands, are noteworthy for demonstrating the intrinsic value of anharmonic calculation for applied spectroscopy. [32][33][34][35][36] Further, a brief note should be made here to point the readers' attention to other potent anharmonic approaches. Those methods can be roughly divided into those oriented at very high accuracy, e.g., vibrational configuration interaction (VCI), 37,38 vibrational coupled cluster (VCC), 39,40 or gridbased methods.…”