# Electric Field and Temperature Effects on the Ab Initio Spectroscopy of Liquid Methanol
## 1 Introduction  
Owing to the presence of a single hydroxyl (OH) group in their molecular structure, monohydric alcohols are very useful systems for the investigation of crucially relevant intermolecular interactions such as hydrogen bonds (H-bonds). Methanol (CH\({}_{3}\)OH) is the smallest organic compound capable of exhibiting and developing H-bonded networks and it is largely employed as an organic solvent in many experimental setups [1, 2]. In this way, liquid methanol samples are widely used in industry and in the fields of organic synthesis, biochemistry and biotechnology [3, 4, 5, 6, 7, 8]. Moreover, the development of direct methanol fuel cells has led, during the last decades, to a broad and continuously growing interest in the understanding of the microscopic properties of methanol [9]. H-bonds in bulk liquid methanol are distinctly different from those typically observed in liquid water. In fact, because of the presence of the hydrophobic methyl (CH\({}_{3}\)) groups, methanol does not give rise to the complexity of the tetrahedral arrangement of the intermolecular interactions present in liquid water. In addition, as the methanol molecule is capable of acting as a donor and, at the same time, as an acceptor of only one H-bond (i.e., each molecule in the bulk is involved in two H-bonds on average), the methanol H-bond network typically gives rise to almost linear structures of interconnected molecules in the liquid phase [10, 11, 12, 13]. Furthermore, methanol molecules are known to be less polar than water molecules, hence establishing weaker H-bonds between each other than water molecules do in neat aqueous solutions. All these properties, conferring to it one of thehighest simplicities of the percolated intermolecular interactions, render liquid methanol the perfect test bed for the general and fundamental understanding of the H-bonds' behavior. Among other things, indeed, methanol represents a typical example of associating fluid, which displays short-range and strongly directional attractive interactions. A plethora of experimental and theoretical studies have ascertained that methanol molecules are bound into linear chains that are sometimes interrupted by the presence of bifurcations [14; 15; 16; 17; 18; 19; 20; 21; 22; 23]. Notwithstanding the huge amount of fundamental and applied spectroscopic investigations under disparate thermodynamic conditions and chemical environments, the bulk liquid methanol infrared (IR) spectrum in the presence of static electric fields has not been reported so far. Owing also to the pioneering work performed by [PERSON] et al. [24; 25], which theoretically and computationally predicted a series of fundamental effects produced by static electric fields on single-molecule systems, some studies on methanol clusters under electric fields have been carried out by using density functional theory (DFT) approaches [26; 27; 28; 29]. Added to the fact that intense electric fields (on the order of 0.1-1.0 V/A or even more [30; 31; 32; 33]) along with quantum-mechanical interactions constitute the foundation of H-bonds and, ultimately, the existence of H-bonded systems, it is also well-known that the application of strong external electric fields can remarkably affect a wide palette of properties of polar fluids [34; 35; 36; 37]. In fact, external electric fields on condensed-phase systems may induce plenty of phenomena, because such fields are able to strongly influence redox- and electron-transfer reactions [38; 39], can affect covalent and intermolecular bonds [40; 41; 42], and can produce the well-known Stark effect [43], as well as the so-called vibrational Stark effect [44; 45] (i.e., the field-induced frequency shift of the molecular vibrations). However, the vibrational Stark effect phenomenon has neither been observed nor investigated in liquid methanol.