TO
MICROWAVE SPECTROSCOPY LABORATORY
Location :
Room No. 449 of the Salt
Current interest :
The ongoing research programmes in the Microwave Spectroscopy Laboratory
are based on the high resolution microwave spectroscopic studies of the gas
phase rotational spectra of organic / inorganic molecules leading to the
determination of their structures, conformations, barrier to internal rotation
and many other features, e.g. electric dipole moment, quadrupole hyperfine
structures etc.
We have worked with some Allyl derivatives and determined their most
predominant conformers in the gas phase. Potential barriers hindering the
internal rotation of the CH3 group have been determined for
different Toluene derivatives from the internal rotation splittings of the
rotational lines. Quadrupole hyperfine structure analysis of 13CF3Br
has been performed. We have also worked with various fluorinated phenols and
benzonitrile compounds.
Currently, we are working with double and triple substituted fluorinated phenol
compounds.
New programme :
1. Construction of a millimeterwave spectrometer for studies of transient molecules
The construction of a millimeterwave spectrometer to study transient molecules of chemical and astrophysical interest has been completed. The spectrometer which, at present, works up to 100 GHz, is basically a source - modulated system combind with a free space discharge cell of 1 meter length and 10 cm diameter. Millimeterwave radiation is produced by using frequency multipliers, the fundamental radiation source being klystrons. Millimeterwave radiation is fed into the absorption cell by a waveguide horn and teflon lens. A similar horn and lens arrangement is used to focus the mmwave power onto the detector after propagating through the cell. The klystron is frequency modulated by a double squarewave of 50 kHz and the signal is detected by a phase sensitive detector in the 2f mode.
The
performance of the spectrometer has been tested by observing many absorption
signals of transient species e.g. CS & FCN, in their ground and different
excited vibrational states. CS was generated inside the cell by a low pressure
(20-30 mtorr) DC discharge ( 1 kv, 50 mA ) of CS2 vapour. Strong 2nd
and 4th harmonic signals were recorded which corresponds to the J=0-->1, and
J=1-->2 signals of CS at 48990.98 MHz and 97980.95 MHz respectively.12C34S,
13C32S signals were also successfully recorded. It may be
metioned here that CS has already been detected in the interstellar space by
radio astronomers. FCN was generated in a low pressure DC discharge of different
fluorobenzonitrile compounds. Two other cyanide compounds e.g., ClCN and BrCN
have also been generated by DC glow discharge technique and their mmwave
spectrum have been anlyzed.
Future plan :
The future aim of this laboratory is to extend the frequency range of investigation and to improve upon the sensitivity and resolution of the newly constructed mmwave spectrometer so that more and more weak signals of transient molecules of astrophysical interest can be detected. For this purpose, digital averaging of the signals and phase locking of the millimeterwave sources has to be achieved. The present room temperature diode detector has to be replaced by InSb liquid helium cooled bolometer detector.
2. Infrared-Radiofrequency (IR-RF) double resonance spectrometer
In
order to study 'pure' nuclear quadrupole hyperfine spectra in the ground and
excited vibrational state of a molecule in the gas phase an IR-RF double
resonance spectrometer has been constructed. An indigenously built CO2
laser was used as the IR radiation source. The spectrometer has been used to
observe 'pure' nuclear quadrupole hyperfine spectra of methyl iodide (CH3I),
a symmetric top molecule with a single quadrupole nucleus.
Facilities available :
(1) Conventional 100 kHz Stark modulated microwave spectrometer with RF-Microwave (MW) and MW-MW double resonance facility.
(2) Millimeterwave spectrometer to study the rotational spectra of transient molecules of chemical and astrophysical interest in the gas phase.
(3) IR-RF double resonance spectrometer.
Selected publications :
(1) Millimeterwave spectrum and ab initio DFT
calculation of the C-gauche conformer of Allyl Isocyanate. A. I. Jaman and P.
R. Bangal. J. Mol. Spectrosc. 255, 134, 2009.
(2)Millimeter-wave spectrum of DC discharge
produced Cyanogen Iodide (ICN) in excited vibrational state. P. R. Varadwaj and
A. I. Jaman.
(3) Time-resolved Fourier transform emission
spectroscopy of laser ablation products. K.
(4) Millimeterwave spectrum of ICN, a transient molecule of chemical and astrophysical interest. A. I. Jaman. J. Phys.: Conference Series. 80, 012006, 2007.
(5) Microwave spectrum of trans 3-fluorophenol in excited torsional states. A. I. Jaman. J. Mol. Spectrosc. 245, 21, 2007.
(6) Millimeter-wave spectrum of 2, 3-difluorobenzonitrile and ab initio DFT calculations. P. R. Varadwaj and A. I. Jaman. J. Mol. Spectrosc. 239, 216, 2006.
(7) Assignment and analysis of the rotational spectrum of 3-chlorobenzonitrile. P. R. Varadwaj, A. I. Jaman, Z. Kisiel and L. Pszczolkowski. J. Mol. Spectrosc. 239, 88, 2006.
(8) Millimeter-wave spectroscopy of chloroacetylene (ClCCH) produced by electrical glow discharge. P. R. Varadwaj and A. I. Jaman. Procd. of Int.Conf.on Submm Sci.&Tech.Allied.Pub. p-97, 2006.
(9) Centrifugal distortion analysis of the millimeter-wave spectrum of 2-fluorobenzonitrile and ab initio DFT calculations. P. R. Varadwaj and A. I. Jaman. J. Mol.Spectrosc. 236, 70, 2006.
(10) Millimeter-wave spectrum of ClCN observed in a DC glow discharge and ab initio calculations. P. R. Varadwaj, P. R. Bangal and A. I. Jaman. J. Mol.Struct. 780-781, 17, 2006.
(11) An ab initio (RHF) and DFT-B3LYP level spectroscopic studies of BrCCCN and the analysis of atomic polar tensors. P. R. Varadwaj and P. R. Bangal. J. Mol. Struct.(Theochem). 730, 23, 2005.
(12) Hydrogen-bonding and protonation effects on the formation of charge transfer complex between para-benzoquinone and 2, 6-dimethoxy phenol. P. R. Bangal. Chem. Phys. Lett. 401, 200, 2005.
(13) Millimeter-wave spectrum of BrCN
produced by a
(14) Infrared-Radiofrequency double resonance
spectrometer: an unique machine to probe excited vibrational states. R. N.
Nandia, A. K. Bhattacharya and A. I. Jaman.
adeceased.
(15) Millimeter-wave spectroscopy of transient molecules produced in a DC discharge. A. I. Jaman. Pramana 61, 85, 2003.
(16) Microwave spectrum of 2,4-Difluorophenol: cis conformer. S. Chakrabarti and A. I. Jaman. J. Mol. Struct. 642, 93, 2002.
(17) Microwave spectrum and quadrupole
coupling constants of 13CF3Br.
(18) Microwave spectrum and quadrupole coupling constants of 2,3-difluorobenzonitrile. M. Onda, T. Kasagi and A. I. Jaman. J. Mol. Struct. 612, 167, 2002.
(19) Microwave spectrum and conformation in 2-Fluorophenylisothiocyanate. S. Chakrabarti and A. I. Jaman. J. Mol. Spectrosc. 202, 223, 2000.
(20) Centrifugal distortion analysis of the microwave spectrum of allyl isothiocyanate (C-gauche Conformer). A. I. Jaman. Pramana 53, 857, 1999.
(21) Microwave spectrum and barrier to internal rotation in Ortho-Tolunitrile. A. I. Jaman, S. Maiti and R. N. Nandi. J. Mol. Spectrosc. 192, 148, 1998.
(22) Microwave spectrum and barrier to internal rotation in 2,4-Difluorotoluene. S. Maiti, A. I. Jaman and R. N. Nandi. J. Mol. Spectrosc. 177, 29, 1996.
(23) Microwave spectrum of Allyl Isothiocyanate: Gauche comformer. S. Maiti, A. I. Jaman and R. N. Nandi. J. Mol. Spectrosc. 165, 168, 1994.
(24) Microwave spectrum of Allyl Isocyanate: Gauche conformer. S. Maiti, A. I. Jaman and R. N. Nandi. J. Mol. Spectrosc. 158, 8, 1993.
Work done in other laboratories :
(1) Submillimeterwave spectra of the AsH and AsD radicals in the X3sigma- electronic state. H. Fujiwara, K. Kobayashi, H. Ozeki, S. Saito and A. I. Jaman. J. Chem. Soc. Faraday Transaction 93(6), 1045, 1997.
(2) Rotational spectra, dipole moment and structure of SiF4--NH3 dimer. R. S. Rouff, T. Emilsson, A. I. Jaman, T. C. Germann and H. S. Gutowsky. J. Chem. Phys. 96, 3441, 1992.
(3) Rotational spectrum and structure of the linear HCN---HCCH dimer. A. I. Jaman, T. C. Germann, H. S. Gutowsky, J. D. Augspurger and C. E. Dykstra Chem. Phys. 154, 281, 1991.
Present Members :
Pradeep Risikrishna Varadwaj (Doctoral Fellow)
E-mail : 
microwave.lab[at]saha.ac.in
This laboratory is currently looking for a young,
energetic and hard working graduate student who is willing to work in the
current and future programmes of this laboratory leading to his/her Ph.D
degree. Strong background in Physics/Physical Chemistry is essential. Must have
a UGC/CSIR fellowship.
Contact E-mail
address : aismail.jaman[at]saha.ac.in