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Infrared Laser Spectroscopy Section (ILSS), PG is carrying out frontline research in the following areas:
■ Infrared spectroscopic studies
• Trace level detection (sub ppm) of molecules/pollutants
• Study of overtone, combination and hot band ro-vibrational molecular transitions
• IR, Raman and surface enhanced spectroscopy of materials
■ Molecular spectroscopy in supersonic molecular beam
• Bonding and electronic structure between a transition metal atom & main group elements

■ Binary metal Cluster Physics Research
• Investigation of geometrical and electronic structure of bi-metallic clusters as a function of
their size and composition



The electronic structure of ScO molecule is simplest among transition metal (TM) bearing molecules. However, even its low temperature spectra are turned out to be quite complex mainly due to various interactions among the excited states. Extensive experimental information is required to validate the benchmark ab initio calculations to get these effects right in the model. We extensively studied the ground and excited electronic states of this molecule at low rotational temperature (30 K).


A new laboratory has been built in the ongoing XII-FYP for studying the physics of free metal clusters. An indigenous dual target dual-laser vaporization/reaction supersonic metal cluster beam setup has been developed. The setup is coupled to an add-on Reflectron Time Of Flight Mass Spectrometer for mass spectrometric investigations. The laboratory is equipped with fixed and tunable lasers from IR to Deep-UV for the laser spectroscopy investigations.
\r\nThe work towards producing a range of pure metal and metal oxide clusters are in progress. We could successfully produce small Aluminium Oxide and Cobalt-Ammonia clusters.


A deep mechanistic insight into the bonding of group-3 metals, Sc, Y, and La with NH has been obtained through a high-level ab initio (CASSCF/MRCI) calculations. Our study reveals that Sc, Y, and La are all bonded to the NH group by a double bond in the π-system which is heavily polarized to the NH for all states.


The quasistatic approximation (QSA) is used to model the field enhancement of isolated triaxial ellipsoidal nanoparticles. The results show the excitation of three distinct plasmonic modes corresponding to the redistribution of polarization charges along each principal axis associated with huge field enhancement.


High resolution near infrared absorption spectra of various weak hot bands of acetylene were recorded at various pressures to obtain the self broadening coefficient. Hot bands arise due to ν₁+ ν₃+ ν₄- ν₄ and to ν₁+ ν₃+ ν₅- ν₅ transition were analysed and subsequently self broadening coefficient of various rotation transitions were obtained.


A classical ABCD matrix based 3D paraxial ray tracing model has been developed to simulate optical reinjection phenomena in linear cavity. The aim of the research is to maximize the intensity enhancement by inserting an astigmatic reinjection mirror in front of the linear cavity.


The SERS results of thiazolidine-2 4-dione (TZD), points to the other aspect of Localized surface plasmon resonance (LSPR) such as plasmon-induced chemical reaction. TZD on Ag NP was found to dimerize by undergoing self-condensation reaction via interfacial indirect transfer of hot-electrons generated by non-radiative decay of LSPR.


This is our first work on metal oxide clusters from molecular spectroscopy laboratory. We could record a mass spectrum of these clusters with metal containing up to 13 atoms. Stoichiometric preference for certain sizes are noticeable. We measured ionization energy for few sizes. A combined experimental & theoretical (DFT) approach enabled us to suggest the geometries of three stable clusters.


Trans-urocanic acid (t-UCA) is found predominantly in the stratum corneum of the human skin (4–34 nM/cm²) and acts as photo protectant against ultraviolet induced DNA damage. On exposure to ultraviolet radiation, t-UCA isomerizes to cis-UCA, and recent studies revealed that the immune-suppressive properties of cis-UCA are linked to skin cancer. SERS, a surface sensitive technique, enabled the detection of t-UCA down to 50 picomolar concentration with good signal to noise ratio.


Sn-124 is needed in weight amount as detector material for neutrinoless double beta decay experiment. The first excited state accessible from the ground state lies in UV at 286.3 nm and have short lifetime of 5 ns. The transition offers a moderate isotope shift (IS) of 441 MHz, however, the availability of high repetition rate (kHz), narrow-band tunable laser in UV having pulse to pulse time jitter ~1 ns is a technological impediment for achieving isotopic selectivity in this transition. Through extensive experimental trials, we have proposed an alternate three-color photoionization scheme using lasers available in the laboratory for the laser separation of Sn-124.


The speciation of borates and silicates introduced by adding different additives are responsible for the varying properties in glasses. Raman and infrared spectroscopy being sensitive probes are used in understanding the subtle changes in the short-range order in two different sets of systems, namely SrO-ZnO-SiO2 (SZS) based glasses and Cs incorporated sodium borosilicate glasses.


The high-resolution Fourier transform spectrum of v₇ fundamental band of CD₃CCH in the spectral range 950–1200 cm⁻¹ have been analyzed. A strong x-y Coriolis interaction with the unseen v₄ state, the l-type interactions and k-type interaction within the v₇ state are taken into account. The overall standard deviation of the fit of about 1700 lines of the transitions up to K = 7 was 0.0007 cm⁻¹. The transitions with K ≥ 8 appear to be perturbed


We found LaNH as a dominant product in the reaction of laser vaporized La and ammonia. This is an important reaction step in the context of oxidation reaction of ammonia with a transition metal atom. We first detected and analyzed C-X band and detected the low-lying ²Δ state found in the isovalent molecules LaO and LaS.


The electronic structure of TiC molecule in ground and excited electronic states, especially at low-energy was not investigated. The accurate experimental data on the ground and low-energy state is required for its detection in carbon-rich circumstellar environment where Ti is detected. The TiC, an early transition metal carbide, is difficult to make and requires tricky experimental conditions to generate in sufficient number density to detect. We generated these molecules in supersonic molecular beam by reaction of laser-produced plasma with methane. The laser-induced excitation spectra yielded accurate molecular constant of the ground X³Σ⁺ and an excited ¹Π state. We detected three low-energy states, predicted theoretically, but undetected hitherto.


Search for the electric dipole moment of a free electron, eEDM, is an intense research topic across many renowned laboratories in the world. Precise molecular constants of the metastable ³Δ state of TaN molecule and the routes to populate this state is important. We have significant contribution in the spectroscopy of this molecule in the form of detecting the spin-components of the ³Δ state and its vibrations.


We have systematically studied the jet-cooled electronic spectra of the NbN molecule in the 18,000-21,000 cm⁻¹ range and determined accurate molecular constants of the electronic states involved in the transitions. The unusual is the observation of a huge spin-orbit asymmetry in the C³Π v = 0 state. We found the spin-orbit interaction between the v = 1 of C³Π₁ and e¹Π states destroyed the symmetric splitting of the C³Π substates. Unusually high 685 cm⁻¹ spin-orbit interaction matrix element between them pushed the C³Π₁ 449 cm⁻¹ (ab initio 244 cm⁻¹) below the C³Π₀ component .


The infrared spectra of different polymorphs of Li₂MnSiO₄, namely, Pmnb (γ) -orthorhombic, Pmn21 (β) - orthorhombic and P21/n (γ) – monoclinic, synthesized by controlled calcination at 500, 750 and 1000 °C respectively, shows differences in arrangement of their respective SiO₄, MnO₄ and LiO₄ units. The edge sharing in Pmnb and P2₁/n polymorphs having sequences Li–Mn–Li and Li-Li-Mn respectively results in the varied features of these polymorphs below 300 cm⁻¹. The isotropic environment of Pmn2₁ offers more or less straight path for Li⁺ migration; responsible for the better electrochemical performance in Pmn2₁ polymorph.



Indigenously developed laser vaporization & reaction based supersonic molecular beam setup for the generation of bi-metallic clusters in gas phase and their investigations using mass spectrometry and laser spectroscopy. The laboratory is equipped with fixed frequency and tunable laser from Deep-UV to IR for laser spectroscopic investigations. The preformed metal clusters can also be soft landed on a range of substrate materials.


External-cavity diode laser (ECDL) based continuous wave tuneable diode laser absorption spectrometer (cw-TDLAS) have recently been developed to carry out various molecular spectroscopic investigations, spectral line shape studies etc. The cw-TDLAS set up coupled with white type absorption cell is capable of recording the spectrum of gaseous sample at low molecular pressure in 1520 nm–1640 nm region at step size of 0.008 nm. Its properties such as narrow line width, tuneability and stability make this ideal source for optical absorption spectroscopy for various atmospheric and astrophysical significant molecules.


Indigenously developed laser ablation/reaction supersonic molecular beam setup for the generation of jet-cooled transition metal-bearing molecules and their electronic structure investigations using laser spectroscopy & mass spectrometry. The laboratory is equipped with various fixed frequency and narrow band tuneable (220-850 nm) lasers to facilitate molecular spectroscopy investigations.

Technologies Developed

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