In Brief

• Supersonic-jet spectroscopy is used to study the structure and dynamics of molecules and molecular clusters that have been cooled to about 10-15 K (far below their boiling points) but remain in the gas phase. Cooling the internal degrees of freedom (molecular rotations and vibrations) through the isenthalpic expansion of the molecular jet with speed higher than the speed of sound in a vacuum produces a highly resolved and simplified electronic and vibrational spectrum. 

• This is one of the very few experimental sets up in India. 

• The spectrometer has been designed and built from scratch by the NISER students, and we have written the data acquisition software.

Salient Features and Advantages

We can…

• Cool down the molecules and molecular clusters to 10-15 K.

• Reduce the spectral broadening and congestion.

• Get high-resolution spectra. The typical FWHM of the excitation spectrum is ~5 cm-1 which is at least 100 times smaller than that of the conventional excitation spectrum obtained in the solution phase.

• Study weak molecular complexes which are not stable at room temperature.

• Record mass-selected and conformation-specific UV and IR spectra. 

• Train students to build scientific instruments.

Challenges to perform the Experiments

• To keep at least six lasers in operation.

• To maintain chamber pressure 10-7 torr.

• To synchronize all the lasers with the pulse valve.

• To have a precise spatial and temporal overlap of UV, and IR beams with the molecular beam inside the vacuum chamber.

• To vaporize the liquid and solid samples without decomposition.

• To keep the channeltron and PMT exactly perpendicular to the point of intersection of the molecular beam and UV and IR beams.  

Salient Features and Advantages

Determining absolute configuration in chiral molecules is a challenging and significant problem for molecular stereochemistry. One of the most popular methods is electronic circular dichroism (ECD). ECD is also very useful in studying different conformations of peptides, proteins, DNA and RNA. The major problem with ECD is that the molecule of interest needs to have chromophore absorbing in the UV-Vis region. There are very few ECD bands in a spectrum, another drawback of ECD being used to extract the absolute configuration of chiral molecules. These limitations can be overcome by using vibrational circular dichroism (VCD). VCD does not need UV-Vis. chromophore. VCD is one of the powerful spectroscopic tools to investigate the self-aggregation of chiral molecules (homocomplexes) and noncovalent interactions of chiral molecules with the guest molecules (heterocomplexes) because of its unique sensitivity to conformational landscapes. However, even sensitive VCD spectra become broad at room temperature when molecules of interest are quite flexible and have many possible conformations and complexes. The combination of matrix isolation (MI) and VCD spectroscopy (MI-CD) is the best alternative to study flexible molecules and weakly bound molecular complexes by trapping them in a cold noble gas matrix (typically ∼10 to 30K), thereby reducing the conformational size and avoiding the solute-solvent interactions. Because of low temperature and lack of solvent broadening, the MI-IR and MI-VCD spectra have much narrower bandwidth than in solution. The sharp spectra are helpful for detailed spectral assignment and conformational distributions. The VCD features can be used for chiral recognition chirality transfer in non-covalently bonded complexes and photoisomerization reactions.

Salient Features 

We are interested to investigate hydrogen bond mediated in/on water catalysis, chiral catalysis, photosensitizers, and fluorescent probes, role of bio-compatible ionic liquids on the structure and function proteins, DNAs and RNAs etc. These need a synthetic laboratory. We have access to fume hoods, rotary evaporators, etc. to carry out simple synthesis.

We are fortunate to avail several common instrumental facilities of our department. Those include

• UV-Vis Spectrophotometer

• Fluorimeter

• Time-Correlated Single Photon Counting (TCSPC)

• Fluorescence up-conversion

• Nuclear Magnetic Resonance Spectrometer (400 MHz, 700 MHz NMR)

• Electron Paramagnetic Resonance Spectrometer (EPR)

• Isothermal Titration Calorimetry (ITC)

• Circular Dichroism Spectrophotometer (CD)

• Electrospray Ionization Mass Spectrometrometry (ESI-MS)