Vibrational and Electronic States of Polyatomic Molecules

In the last few years, theoretical results have been obtained in:

- electronic non-radiative transitions in isolated molecules;

- a method has been developed for calculation of highly excited vibration states in polyatomic molecules and study of the vibration relaxation of these states.

Prof. DSc. Svetoslav Rashev

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Born 1948, in Bourgas, Bulgaria.

Graduated Sofia University, Physical Department, 1973.

PhD, Karpov Institute of Physical Chemistry, Moscow, 1983. Supervisor: Professor Victor G. Plotnikov.

Dr. of Sciences, 1996, at ISSP BAS.

Employed at the Institute of Solid State Physics at the Bulgarian Academy of Sciences (ISSP BAS), Department for Optics&Spectroscopy, since 1973.

Present position: Professor.

Main Fields of Theoretical Research Activity:

             Molecular Spectroscopy,
             Molecular Vibrational Dynamics and Relaxation,
             Electronic Radiationless Transitions in Isolated Polyatomic Molecules,
             Molecular Symmetry,
             Large Scale Vibrational Calculations,

 

                                RECENT    AND   PRESENT   RESEARCH   ACTIVITY
  Theoretical work has been done in the recent years, on the construction and elaboration of a vibrational procedure and computer code, designed for implementation of large scale vibrational calculations on formaldehyde H2CO and thiophosgene Cl2CS. The procedure is based on the following key ideas:

-- Combined local modes/symmetrized modes formalism (LM/SM), for the molecular vibrational modes; we employ an exact expression for the molecular kinetic energy operator and a quartic potential energy surface (PES); the force constants of the quartic PES have been originally obtained using high level ab initio computations [with the nwchem suite of ab initio programs, using a cc-p VTZ correlation consistent polarized triple valence basis, further corrected for electron correlation by CCSD(T)]; next, the ab initio calculated quadratic, cubic and quartic force constants were refined, using our large scale variational method and a nonlinear least squares fitting algorithm and comparing our calculated frequencies to the experimentally measured frequencies of formaldehyde and thiophosgene.

--  The employed vibrational calculation procedure is variational; it is based on an artficial intelligence (AI) search algorithm for selecting the appropriate active space (AS) of basis states and setting up the relevant Hamiltonian matrix. In order to obtain the required molecular vibrational energy levels, the Hamiltonian matrix is diagonalized numerically, using a Lanczos tridiagonalization routine. The dimensionality of the obtained Hamiltonian matrices may amount to 100000 or larger.

-- Using the vibrational procedure and code, large scale calculations have been performed on the vibrational frequencies of ground electronic state formaldehyde and thiophosgene both in the lower excitation domain, where we obtained very good coincidence of the theoretically calculated and the experimentally measured frequencies, as well as in the highly excited vibrational excitation energy range, to explore the characteristics of IVR and vibrational level mixing.

-- In particular for S0 thiophosgene, we have been able to extend the large scale vibrational calculations up to the dissociation limit at ~20000 cm-1, where we compared our results on the features IVR and vibrational isolation with the recent spectroscopic measurements on “feature” states as well as with the conclusions derived from local coupling models by other authors.

 
 


 

                                                SOME  PUBLICATIONS
 

S. Rashev and D. C. Moule, Spectrochim. Acta A: Mol. Biomol. Spectr. 140, p.305-310 (2015).

“A Refined Quartic Potential Energy Surface and large scale vibrational calculations for S0 Thiophosgene.”

S. Rashev and D. C. Moule, Prog. Theoret. Chem. Phys. B27: Advances in Quantum Methods and Applications in Chemistry, Physics, and Biology, Chapter 8, p.141-160 (Springer, 2013).

“A Refined Quartic Potential Energy Surface for S0 Formaldehyde.”

S. Rashev and D. C. Moule, J. Molec. Spectrosc. 286-287, p.21-29 (2013).

“Large Scale Variational Calculations on the Vibrational Level Structure and Vibrational Mixing in S0 HDCO up to Very High Excitation Energies.”

S.Rashev, D.C.Moule and V.Rashev, Spectrochim.Acta A: Mol.Biomol.Spectr. 97, p.111-118 (2012).

“Variational Study on the Vibrational Level Structure and Vibrational Level Mixing of Highly Vibrationally Excited S0 D2CO.”

S.Rashev and D.C.Moule, Spectrochim.Acta A: Mol.Biomol.Spectr. 87, 286-292 (2012).

“Variational Study on the Vibrational Level Structure and IVR Behavior of Highly Vibrationally Excited S0 Formaldehyde.”

S. Rashev, D.C. Moule and R.H. Judge, Int.J.Quant.Chem. 111 (2), 279-287 (2011).

“The Role of Rotational Relaxation in the Intersystem Crossing Between a Triplet and a Singlet Electronic State.”

S. Rashev and D.C. Moule, J. Chem. Phys., 130(13), 134307 (2009).

“Rotational Level Involvement in the T1→S0  Intersystem Crossing Transition in Thiophosgene.”

S. Rashev and D.C. Moule, J. Chem. Phys., 128(9), 31295391 (2008).

 “A Combined Theoretical Treatment of   Intersystem Crossing and Intramolecular Vibrational Redistribution in Thiophosgene”.

 

S. Rashev, D.C. Moule and S. Djambova, Chem. Phys. Letters, 441(1-3), pp.43-47 (2007). 

 “On the T1→S0 Intersystem Crossing Rate Constant in Thiophosgene”.

 

S. Rashev, I.M. Bivas and D.C. Moule, Chem. Phys. Letters, 438 (4-6), pp.153-156 (2007).

“Large Scale Vibrational Hamiltonian Calculations on Thiophosgene”.

 

S. Rashev, D.C. Moule and S. Djambova, J. Phys. Chem. A  110 (51), p.13769-13774 (2006).

 “Empirical Determination of  The Harmonic Force Constants in Benzene. 4. The Fermi Resonances”.

 

S. Rashev and D.C. Moule, J. Molec. Spectrosc. 235 (1), pp.93-103 (2006).
“Hamiltonian description and 6D calculations on the ammonia vibrational levels”.

S. Rashev, Recent Research Developments in Physical Chemistry, Transworld Research Network, 37/661 (2), p.279-308 (2004).
“Large Scale Quantum Mechanical Calculations on the Benzene Vibrational System”.

S. Rashev and D.C. Moule, J. Phys. Chem. A  108 (7), p.1259-1267 (2004).
“Empirical Determination of  The Harmonic Force Constants in Benzene. 3. The Harmonic Frequencies.”

S. Rashev, Int. J. Quantum Chem. 99 (6), p.894-902 (2004).
“Determination of an improved set of harmonic force constants for benzene”.
 
       S. Rashev and D.C. Moule, Chem. Phys. 295 (2), p.109-117 (2003).
      “Calculations on the Vibrational Level Density in Formaldehyde.”
 
       S. Rashev, J. Phys. Chem. A 107 (13), p.2160-2171 (2003).
      “Empirical Determination of  The Harmonic Force Constants in Benzene. 2. The C-H Stretch System.”

       S. Rashev, Int. J. Quantum Chem. 89 (4), p. 292-298 (2002).
      “Complex Symmetrized Analysis of Benzene Vibrations”.

      S. Rashev, J. Phys. Chem. A 105 (26), p. 6499-6505 (2001).
      “On the Empirical Determination of  Some Harmonic and Anharmonic Force Constants in Benzene”.