Staff 
Ovsyannikov Roman Ilyich Education: Scope of professional interests: Professional career: Awards, prizes, grants: Pedagogical activities: Publications: Most significant papers and results: 1. R. I. Ovsyannikov and M. Yu. Tret'yakov, Determination of Loss in a FabriPerot Resonator from Its Response to Exciting Radiation of a FastScanned Frequency, Journal of Communications Technology and Electronics, Vol. 50, No. 12, 2005, pp. 14001408. The response of a highQ Fabri–Perot resonator to exciting radiation with a frequency that is fast digitally scanned and a phase that exhibits no jumps during switchings is simulated. The inverse problem of determination of the parameters of the resonator from the shape of its response is solved. Solution of the problem is important for precision measurements of the decay parameter of millimeter and submillimeterwave radiation in dielectrics. Such measurements have become possible with the advent of modern fast frequency synthesizers. The developed algorithm is applied to optimize the experimental conditions. 2. S.V.Shirin, O.L.Polyansky, N.F.Zobov, R.I. Ovsyannikov, A.G. Csaszar, J.Tennyson, Spectroscopically determined potential energy surfaces of the H_{2}^{16}O, H_{2}^{17}O and H_{2}^{18}O Isotopologues of water, Journal of Molecular Spectroscopy 236, 216223 (2006). Adiabatic potential energy surfaces (PESs) for three major isotopologues of water, H_{2}^{16}O, H_{2}^{17}O, and H_{2}^{18}O, are constructed by fit ting to observed vibration–rotation energy levels of the system using the nuclear motion program DVR3D employing an exact kinetic energy operator. Extensive tests show that the massdependent ab initio surfaces due to Polyansky et al. [O.L. Polyansky, A.G. Csaszar, S.V. Shirin, N.F. Zobov, P. Barletta, J. Tennyson, D.W. Schwenke, P.J. Knowles, Science 299 (2003) 539–542.] provide an excellent starting point for the fits. The refinements are performed using a massindependent morphing function, which smoothly distorts the original adiabatic ab initio PESs. The best overall fit is based on 1788 experimental energy levels with the rotational quantum number J = 0, 2, and 5. It reproduces these levels with a standard deviation of 0.079 cm1 and gives, when explicit allowance is made for nonadiabatic rotational effects, excellent predictions for levels up to J = 40. Theoretical linelists for all three isotopologues of water involved in the PES construction were calculated up to 26 000 cm^{1} with energy levels up to J = 10. These linelists should make an excellent starting point for spectroscopic modelling and analysis. 3. N.F. Zobov, R.I. Ovsyannikov, S.V. Shirin, O.L. Polyansky, J.Tennyson, A. Janka and P.F. Bernath, Infrared emission spectrum of hot D2O, J. Mol. Spectrosc., 240, 132139 (2006). An emission spectrum of hot D2O (15000C) has been analyzed in the 20774323 cm^{1} region. A considerable number of new vibrationrotation energy levels have been determined and two new vibrational levels identified. The new (041) and (022) vibrational levels have estimated band origins of 7343.93±0.01 cm^{1} and 7826.38±0.02, respectively. 4. N.F. Zobov, R.I. Ovsyannikov, S.V. Shirin, O.L. Polyansky, The Assignment of Quantum Numbers in the Theoretical Spectra of the H216O, H217O, and H_{2}^{18}O Molecules Calculated by Variational Methods in the Region 026000 cm1, Optics and Spectroscopy, 102, N3, 348353 (2007). Quantum numbers have been assigned in the theoretical spectra of three isotopologues of the water molecule: H_{2}^{16}O, H_{2}^{17}O, and H_{2}^{18}O. The spectra were calculated by variational methods in the region 0– 26000 cm–1 at a temperature of 296 K. For each molecule, the quantum numbers are assigned to more than28000 levels. The quantum numbers are assigned to 216766, 210679, and 211073 spectral lines of the H_{2}^{16}O, H_{2}^{17}O, H_{2}^{18}O molecules, respectively. 5. Sergei V. Shirin, Nikolay F. Zobov, Roman I. Ovsyannikov, Oleg L. Polyansky and Jonathan Tennyson,Water line lists close to experimental accuracy using a spectroscopically determined potential energy surface for H_{2}^{16}O, H_{2}^{17}O, and H_{2}^{18}O, J. Chem. Phys., 128, 224306 (2008). DOI: 10.1063/1.2927903 Line lists of vibrationrotation transitions for the H_{2}^{16}O, H_{2}^{17}O, and H_{2}^{18}O isotopologues of the water molecule are calculated, which cover the frequency region of 0 – 20 000 cm−1 and with rotational states up to J = 20 (J = 30 for H_{2}^{16}O). These variational calculations are based on a new semitheoretical potential energy surface obtained by morphing a high accuracy ab initio potential using experimental energy levels. This potential reproduces the energy levels with J = 0, 2, and 5 used in the fit with a standard deviation of 0.025 cm^{−1}. Linestrengths are obtained using an ab initio dipole moment surface. That these line lists make an excellent starting point for spectroscopic 6. Nikolai F. Zobov, Sergei V. Shirin, Roman I. Ovsyannikov, Oleg L. Polyansky, Robert J. Barber, Jonathan Tennyson, Peter F. Bernath, Michel Carleer, Reginald Colin and PierreFrançois Coheur, Spectrum of hot water in the 4750  13,000 cm^{−1} wavenumber range (0.7692.1 µm) MNRAS, 387, 10931098 (2008). The high resolution laboratory spectrum of hot water vapour has been recorded in the 500– 13 000cm^{−1} wavenumber range and we report on the analysis of the 4750–13 000cm^{−1} (0.769–2.1 μm) portion. The emission spectrum was recorded using an oxyacetylene welding torch and a Fourier transform spectrometer. Line assignments in the laboratory spectrum as well as in an absorption spectrum of a sunspot umbra were made with the help of the BT2 linelist. Our torch spectrum is the first laboratory observation of the 9300 Å ‘steam bands’ seen in Mstars and brown dwarfs. 7. Roman I. Ovsyannikov, Walter Thiel, Sergei N. Yurchenko, Miguel Carvajal, and Per Jensen, Vibrational energies of PH3 calculated variationally at the complete basis set limit, J. Chem. Phys., 129, 044309 (2008). DOI: 10.1063/1.2956488 The potential energy surface (PES) for the electronic ground state of PH3 was calculated at the CCSD(T) level using augccpV(Q + d)Z and augccpVQZ basis sets for P and H, respectively, with scalar relativistic corrections included. A parametrized function was fitted through these ab initio points, and one parameter of this function was empirically adjusted. This analytical PES was employed in variational calculations of vibrational energies with the newly developed program TROVE. The convergence of the calculated vibrational energies with increasing vibrational basis set size was improved by means of an extrapolation scheme analogous to the complete basis set limit schemes used in ab initio electronic structure calculations. The resulting theoretical energy values are in excellent agreement with the available experimentally derived values. 8. Roman I. Ovsyannikov, Walter Thiel, Sergei N. Yurchenko, Miguel Carvajal, Per Jensen, PH3 revisited: Theoretical transition moments for the vibrational transitions below 7000 cm1, J. Mol. Spectrosc, 252, 2, (2008) 121128. DOI: 10.1016/j.jms.2008.07.005 We present here an extensive list of theoretical vibrational transition moments for the electronic ground state of PH_{3}, covering all transitions with significant intensities in the wavenumber region below 7000 cm^{1} . This work complements, and uses a potential energy surface from, our recent calculation of vibrational term values for PH_{3} [R.I. Ovsyannikov, W. Thiel, S.N. Yurchenko, M. Carvajal, P. Jensen, J. Chem. Phys. 129 (2008) 044309] and it extends, and uses a dipole moment surface from, our previous work on PH3 intensities [S.N. Yurchenko, M. Carvajal, W. Thiel, P. Jensen, J. Mol. Spectrosc. 239 (2006) 71–87]. 9. Roman I. Ovsyannikov, Vladlen V. Melnikov, Walter Thiel, Per Jensen, Oliver Baum, Thomas F. Giesen, and Sergei N. Yurchenko, Theoretical rotationtorsion energies of HSOH, J. Chem. Phys, 129, 154314 (2008). DOI: 10.1063/1.2992050 The rotationtorsion energies in the electronic ground state of HSOH are obtained in variational calculations based on a newly computed ab initio CCSD(T)/augccpV(Q + d)Z potential energy surface. Using the concept of the reaction path Hamiltonian, as implemented in the program TROVE (theoretical rovibrational energies), the rotationvibration Hamiltonian is expanded around geometries on the torsional minimum energy path of HSOH. The calculated values of the torsionalsplittings are in excellent agreement with experiment; the rootmeansquare (rms) deviation is 0.0002 cm^{−1} for all experimentally derived splittings (with J ≤ 40 and K_{a} ≤ 4). The model provides reliable predictions for splittings not yet observed. The available experimentally derived torsionrotation term values (with J ≤ 40 and K_{a} ≤ 4) are reproduced ab initio with an rms deviation 10. R. I. Ovsyannikov, P. Jensen, M. Yu. Tretyakov, and S. N. Yurchenko, On the Use of the Finite Difference Method in a Calculation of Vibration–Rotation Energies , Optics and Spectroscopy , 107, № 2, с. 211–227 (2009). DOI: 10.1134/S0030400X09080104 The use of the finite difference method to obtain a Taylor series expansion of a potential energy function for a subsequent calculation of the rovibration energies of molecules is considered. A method is proposed that allows the stability of a finite difference scheme to be increased against the computational inaccuracy upon numerical expansion of a multidimensional potential energy function into a high order Taylor series. The method is based on the successive elimination of calculated expansion coefficients of a higher order in calculating the lower order coefficients by the finite difference method. The approach is illustrated for the example of the CO and H2S molecules. 11. Sergei N. Yurchenko, Roman I. Ovsyannikov, Walter Thiel, Per Jensen, Rotation–vibration energy cluster formation in XH_{2}D and XHD_{2} molecules (X = Bi, P, and Sb), J. Mol. Spectrosc, 256, 119127 (2009). DOI: 10.1016/j.jms.2009.03.001 We investigate theoretically the energy cluster formation in highly excited rotational states of several pyramidalXH_{2}D and XHD_{2} molecules (X = Bi, P, and Sb) by calculating, in a variational approach, the rotational energy levels in the vibrational ground states of these species for J ≤ 70. We show that at high J thecalculated energy levels of the dideuterated species XHD_{2} exhibit distinct fourfold cluster patterns highly similar to those observed for H_{2}X molecules. We conclude from eigenfunction analysis that in the energy cluster states, the XHD2 molecule rotates about a socalled localization axis which is approximately parallel to one of the X–D bonds. For the monodeuterated XH2D isotopologues, the rotationalspectra are found to have a simple rigidrotor structure with twofold clusters. 12. N.F. Zobov, S.V. Shirin, R.I. Ovsyannikov, O.L. Polyansky, S.N. Yurchenko, R.J. Barber, J. Tennyson, R.J. Hargreaves, P.F. Bernath, Analysis of high temperature ammonia spectra from 780 to 2100 cm1, J. Mol. Spectrosc, 269, 104108 (2011). DOI: 10.1016/j.jms.2011.05.003 A recentlyrecorded set [Hargreaves et al., Astrophys. J., in press] of Fourier transform emission spectra of hot ammonia is analyzed using a variational line list. Approximately 3350 lines are newly assigned to mainly hot bands from vibrational states as high as v2 = 2. 431 new energy levels of these states are experimentally determined, considerably extending the range of known rotationallyexcited states. Comparisons with a recent study of high J levels in the ground and first vibrational states [Yu et al., J. Chem. Phys., 133 (2010) 174317] suggests that while the line assignments presented in that work are correct, their energy level predictions suffer from problems associated with the use of very highorder perturbation series in the effective Hamiltonian. It is suggested that variational calculations provide a more stable method for analyzing spectra involving highlyexcited states of ammonia. 13. Oleg L. Polyansky, Alexander Alijah, Nikolai F. Zobov, Irina I. Mizus, Roman I. Ovsyannikov, Jonathan Tennyson, Lorenzo Lodi, Tamas Szidarovsky, Attila G. Császár, The molecular ion H3+ is the simplest polyatomic and polyelectronic molecular system, and its spectrum constitutes an important benchmark for which precise answers can 14. Oleg L. Polyansky, Roman I. Ovsyannikov, Aleksandra A. Kyuberis, Lorenzo Lodi, Jonathan Tennyson, Nikolai F. Zobov, Calculation of Rotationvibration Energy Levels of the Water Molecule with NearExperimental Accuracy Based on an ab Initio Potential Energy Surface, The Journal of Physical Chemistry A, 2013, 117 (39), 9633–9643. DOI: 10.1021/jp312343z A recently computed, highaccuracy ab initio Born−Oppenheimer (BO) potential energy surface (PES) for the water molecule is combined with relativistic, adiabatic, quantum electrodynamics, and, crucially, nonadiabatic corrections. Calculations of rovibrational levels are presented for several water isotopologues and shown to have unprecedented 15. Oleg L. Polyansky, Igor N. Kozin, Roman I. Ovsyannikov, Pawel Malyszek, Jacek Koput, Jonathan Tennyson, and Sergei N. Yurchenko, Variational Calculation of Highly Excited Rovibrational Energy Levels of H2O2, The Journal of Physical Chemistry A, 2013, 117 (32), 7367–7377. DOI: 10.1021/jp401216g Results are presented for highly accurate ab initio variational calculation of the rotation  vibration energy levels of H_{2}O_{2} in its electronic ground state. These results use a recently computed potential energy surface and the variational nuclearmotion programmes WARV4, which uses an exact kinetic energy (EKE) operator, and TROVE, which uses a numerical expansion for the kinetic energy. The TROVE calculations are performed for levels with high values of rotational excitation, J up to 35. The purely ab initio calculations of the rovibrational energy levels reproduce the observed levels with a standard deviation of about 1 cm^{−1},similar to that of the J = 0 calculation as the discrepancy between theory and experiment for rotational energies within a given vibrational state is substantially determined by the error in the vibrational band origin. Minor adjustments are made to the ab initio equilibrium geometry and to the height of the torsional barrier. Using these and correcting the band origins using the error in J = 0 states lowers the standard deviation of the observed − calculated energies to only 0.002 cm^{−1} for levels up to J = 10 and 0.02 cm^{−1} for all experimentally know energy levels, which extend up to J = 35. 16. Roman I. Ovsyannikov, Tsuneo Hirano, and Per Jensen, The Renner Effect in the X? ^{2}A″ and Ã^{2}A′ Electronic States of HSO/HOS, The Journal of Physical Chemistry A, (2013). DOI: 10.1021/jp406940w We report a theoretical investigation of the X?^{2}A″ and Ã^{2}A' electronic states of HSO/HOS. Threedimensional potential energy surfaces for the X?^{2}A″ and Ã^{2}A' electronic states of HSO/HOS have been calculated ab initio by the corevalence MRSDCI+Q/[augccpCVQZ(S,O),augccpVQZ(H)] method, and nearglobal potential energy surfaces have been constructed. These surfaces have been used, in conjunction with our computer program DR, for calculating HSO/HOS rovibronic energies in the electronic states X?^{2}A″ and Ã^{2}A'. Both electronic states have nonlinear equilibrium geometries and they correlate with 2Π states at the HSO and HOS linear configurations so that they exhibit the double Renner effect. The present DR calculation of the rovibronic energies for the X?^{2}A″ and Ã^{2}A' electronic states of HSO/HOS is complicated by the Rennerinteraction breakdown of the BornOppenheimer approximation and by HSO/HOS isomerization. Calculated energies are reported together with analyses of the rovibronic wave functions for selected states. These analyses explore the interplay between the effects of, on one hand, Renner interaction and, on the other hand, isomerization tunneling in the rovibronic dynamics of HSO/HOS.

