Computational Techniques for Analytical Chemistry and Bioanalysis

ALONSO DE ARMIÑO, DIEGO J.; GONZALEZ LEBRERO, MARIANO CAMILO; SCHERLIS, DAMIÁN A.; DARÍO A. ESTRIN

Royal Society of Chemistry

Año: 2020 p. 55

978-1-78801-461-8

Vibrational spectroscopy is without a doubt among the most importantand versatile experimental techniques available today in the chemicalsciences. From infrared (IR) spectroscopy to all possible variants ofRaman spectroscopy, including resonant Raman, coherent anti-StokesRaman spectroscopy (CARS), stimulated Raman spectroscopy (SRS),surface-enhanced Raman spectroscopy (SERS), and of course the morerecent bidimensional techniques, which sometimes even combinevibrational with electronic spectroscopy. All of these techniques probethe structure of matter as a function of the structure of its vibrationalenergy levels, as well as the interactions between them. Modern experimental techniques have achieved an outstanding level of accuracy, forexample in the gas phase, in rare-gas matrix isolation spectroscopy or,more recently, in superfluid helium nanodroplets, which in many casescall for high precision theoretical methods to aid in the interpretation ofexperimental results. Moreover, rotational and vibrational techniques arecentral to the study of organic molecules in the interstellar medium or inthe atmosphere of other celestial bodies. The Cassini?Huygens mission,for example, probed the atmosphere of Titan (one of Saturn?s moons)and demostrated that simple molecules in the gas phase can producecomplex organic molecules, particularly pre-biotic molecules,1 andalthough many molecular species have been detected, there are stillmany more waiting for identification, as many signals obtained withCassini?s composite infrared spectrometer (CIRS) have not yet been assigned.2 Vibrational spectroscopy is also a paramount tool in the study ofcomplex systems such as those found in material and biological sciences. The modelling of these kinds of systems is very challenging, asthe model in question must not only be able to reproduce the vibrationalstructure of the solute in great detail, but also its interactions with a richand complicated environment.In this chapter, we present a review of the theoretical techniques used todeal with a wide variety of scenarios in the context of the modelization ofthe vibrational properties of molecular systems. In Section 3.2.1 we startwith a brief introduction to vibrational structure theory at its most basiclevel, (i.e. harmonic approximation) as well as intensity calculations forRaman and infrared spectroscopies. Section 3.3 deals with advancedvibrational structural methods for high accuracy anharmonic calculationof vibrational spectra. This section encompases the theoretical introduction to the basic theory of the diverse theoretical approximations to thesolutions of the nuclear Schro¨dinger equation, as well as different representations of the potential energy surface, and the kinetic energy operator.The section ends with a review of the latest developments in the field andtheir applications. Section 3.4 is concerned with the simulation of vibrational spectroscopies in complex environments, with a special emphasison hybrid quantum mechanical-molecular mechanical methodologies,together with a review of selected applications. Special attention is devotedto simulation methods for SERS and related techniques.