Although the nature around us is full of stable molecules in which the atoms are held together with covalent bonds, it is the weak forces such as van der Waal’s and electrostatic that govern their mutual interactions and hence lend them the properties that they exhibit.  Hydrogen bonding interaction is omnipresent and has been an active area of investigation for several decades.  Although much is known about the classical H-bonds, there is still a lot more to be discovered.  Besides the familiar H-bonding players such molecules containing O, N, and halogen atoms, the carbon and sulfur centered H-bonds are equally important.  Our research focuses on investigations of such novel H-bonds on the microscopic scale.  The specific questions that we ask are their structural properties, relative strengths, nature of dominating forces (electrostatics vs dispersion), behavior in the neutral ground and excited states as well as the cationic state.  Another aspect of the concern is determination of the exact binding energies of these complexes.

Conventional HB is generally depicted as XH---Y where the hydrogen atom covalently bound to an electronegative atom X is shared between atoms X and another electronegative atom Y by electrostatic interaction.  The stretching mode vibrational frequency of the HB donor XH red shifts substantially indicating weakening of the bond and the XH---Y structure is fairly linear.  In the last couple of decades several new type of hydrogen bonds have been reported, viz., i) XH‑‑‑f type hydrogen bonds, where the HB acceptor is the pi electron density of aromatic compounds rather than some electronegative atom Y, ii) CH---Y type of hydrogen bonds where contrary to the conventional observation, the XH stretching frequency actually blue shifts, and iii) sulfur centered hydrogen bonds which have been condemned as very weak hydrogen bond players and were never paid any attention.