Welcome to

Prof. P. K. Das's Research Group

Prof. Puspendu K. Das

Department of Inorganic & Physical Chemistry

Indian Institute of Science, Bangalore

E- mail: pkdas@iisc.ac.in

Research Interests

(a) Nonlinear optics

The central objective of our group is to use single and two laser based spectroscopic techniques to probe molecular properties. In the area of molecular nonlinear optics our aim is to exploit second harmonic light scattering as a probe for bulk physical properties of molecules in solution. Intensity of incoherently scattered SH light is proportional to the square of molecular hyperpolarizability (β) which changes with a physical process as well as symmetry of the molecular species in solution. Using this principle we measure second harmonic light scattering intensity and relate it to the property which is responsible for causing the change.

Chemical application of second harmonic light scattering is a very active area in our group. Polarization resolved second harmonic scattering has been used to obtain geometry of weak (1-10 kcal/mol) molecular complexes in solution for which no technique other than small angle neutron scattering is available. The origin of large second harmonic generation in noble metal nanoparticle of 5-100 nm diameter is another area of investigation where we have probed the origin of nonlinearity in these systems. We are currently interested in studying the thermodynamics of adsorption of proteins and nucleic acids on nanoparticle surfaces. Studying protein-protein interaction at nanomolar concentrations by SHLS is another area of focus in our group.

(b) Infrared Spectroscopy and atmospheric Chemistry

In the area of atmospheric and environmental chemistry our research efforts are directed to detection of polycyclic aromatic hydrocarbons (PAH) and their photolysis products at low concentrations by FT-IR spectroscopy. In the high frequency mid-IR region we are now trying to develop an effective spectroscopic Hamiltonian to identify vibrational peaks resulting from Fermi Type I and Type II coupling mechanisms. It is also found that hetero atom substitution in an organic ring enhances the Fermi coupling constants.