Sotir Chervenkov | Max-Planck Institute for Quantum Optics (original) (raw)

Uploads

Papers by Sotir Chervenkov

Research paper thumbnail of Conformation Study of Ephedrine and 2-PHENYLETHANOL and Their Hydrated Clusters by Mass Selective High-Resolution Uv Spectroscopy and Ab Initio Calculations

A promising approach to the understanding of the interaction mechanisms and intrinsic properties ... more A promising approach to the understanding of the interaction mechanisms and intrinsic properties of biological systems is the spectroscopic investigation of their conformational structures and dynamics at molecular level in the gas phase. Recently we measured the first resonance-enhanced two-photon ionization (R2PI) spectra with rotational resolution (70 MHz FWHM laser bandwidth) and mass selection of almost all vibronic bands of the S

Research paper thumbnail of Continuous Centrifuge Decelerator for Polar Molecules

Physical Review Letters, 2014

Producing large samples of slow molecules from thermal-velocity ensembles is a formidable challen... more Producing large samples of slow molecules from thermal-velocity ensembles is a formidable challenge. Here we employ a centrifugal force to produce a continuous molecular beam with a high flux at near-zero velocities. We demonstrate deceleration of three electrically guided molecular species, CH 3 F, CF 3 H, and CF 3 CCH, with input velocities of up to 200 m s À1 to obtain beams with velocities below 15 m s À1 and intensities of several 10 9 mm À2 s À1. The centrifuge decelerator is easy to operate and can, in principle, slow down any guidable particle. It has the potential to become a standard technique for continuous deceleration of molecules.

Research paper thumbnail of High-Resolution Mass-Selective UV Spectroscopy of Pseudoephedrine: Evidence for Conformer-Specific Fragmentation

The Journal of Physical Chemistry A, 2011

Research paper thumbnail of genehmigten Dissertation

2. Univ.-Prof. Dr. Dr. h. c. A. Laubereau Die Dissertation wurde am 05.03.2007 bei der Technische... more 2. Univ.-Prof. Dr. Dr. h. c. A. Laubereau Die Dissertation wurde am 05.03.2007 bei der Technischen Universität München eingereicht und durch die Fakultät für Chemie am 29.03.2007 angenommen. 2 To the memory of my father,

Research paper thumbnail of Stopping intense beams of internally cold molecules via centrifugal forces

Bulletin of the American Physical Society, 2016

Research paper thumbnail of Investigation of Weak Intra- and Intermolecular Interactions and Conformational Structures of Flexible Molecules and Complexes by Mass Selective High Resolution Resonance Enhanced Two Photon Ionization Laser Spectroscopy

The goal of the work is to investigate intra- and intermolecular weak interactions and the subtle... more The goal of the work is to investigate intra- and intermolecular weak interactions and the subtle interplay between them, including hydrogen and dispersion bonds stabilizing conformeric structures of flexible molecules and small complexes. Accurate rotational constants and transition moment ratio are obtained by a combination of mass-selective rotationally resolved two-photon two-color resonance-enhanced ionization spectroscopy of cold molecular beams, rotational spectra fitting technique based on genetic algorithms, and high-level quantum chemistry ab initio calculations. The studied model species include two groups: i) complexes of water, acetylene, and argon with a molecule pertaining two conjugated π-electron systems, leading to a strong electron density delocalization: styrene and its fluorinated derivative; and ii) the flexible biologically relevant molecule 2-phenylethanol and its complex with argon, and the neurotransmitter ephedrine. The assigned gauche structure of 2-pheny...

Research paper thumbnail of A Road Map to Ultracold Polyatomic Molecules

Research paper thumbnail of Internal-state thermometry of cold polyatomic molecules

Bulletin of the American Physical Society, 2016

Research paper thumbnail of A Centrifuge Decelerator: Slowing down Continuous Beams of Polar Molecules by an Inertial Force

Bulletin of the American Physical Society, 2013

Research paper thumbnail of Electrically guided continuous supersonic beams of polar molecules from a cryogenic buffer-gas source

Bulletin of the American Physical Society, 2012

Submitted for the DAMOP12 Meeting of The American Physical Society Electrically guided continuous... more Submitted for the DAMOP12 Meeting of The American Physical Society Electrically guided continuous supersonic beams of polar molecules from a cryogenic buffer-gas source XING WU, CHRISTIAN SOMMER, SOTIR CHERVENKOV, ANDREAS ROHLFES, MARTIN ZEPPENFELD, LAURENS VAN BUUREN, GERHARD REMPE, Max-Planck-Institut für Quantenoptik — In order to obtain dense samples of internally and translationally cold polar molecules, we use the method of buffer-gas cooling [1], combined with supersonic expansion. We have demonstrated that when the cryogenic buffer-gas cell is operated in a supersonic regime, molecular fluxes are hydrodynamically enhanced by up to two orders of magnitude. Meanwhile, the translational velocity profile of the output molecular beam is cooled to beyond Mach number 6 via supersonic expansion. Due to the cryogenic cell temperature, the forward velocity of the supersonic molecular beam is below 190m/s. The low-field-seeking molecules in the so-produced continuous supersonic beam ar...

Research paper thumbnail of A high density source of cold, slow and rotationally pure polar molecules

Research paper thumbnail of Observation of cold dipolar collisions between centrifuge decelerated molecules

Research paper thumbnail of A cryofuge for cold-collision experiments with slow polar molecules

Science (New York, N.Y.), Jan 3, 2017

Ultracold molecules represent a fascinating research frontier in physics and chemistry, but it ha... more Ultracold molecules represent a fascinating research frontier in physics and chemistry, but it has proven challenging to prepare dense samples at low velocities. Here, we present a solution to this goal by means of a nonconventional approach dubbed cryofuge. It uses centrifugal force to bring cryogenically cooled molecules to kinetic energies below 1 K × kB in the laboratory frame, where kB is the Boltzmann constant, with corresponding fluxes exceeding 1010 per second at velocities below 20 meters per second. By attaining densities higher than 109 per cubic centimeter and interaction times longer than 25 milliseconds in samples of fluoromethane as well as deuterated ammonia, we observed cold dipolar collisions between molecules and determined their collision cross sections.

Research paper thumbnail of Back Cover: Thermometry of Guided Molecular Beams from a Cryogenic Buffer-Gas Cell (ChemPhysChem 22/2016)

Research paper thumbnail of Mass analysed threshold ionisation spectroscopy of flexible 2-para-fluorophenylethanol conformers with and without an intramolecular OH⋯π bond

Physical Chemistry Chemical Physics, 2009

The cationic state of the prototype flexible molecule 2-para-fluorophenylethanol has been investi... more The cationic state of the prototype flexible molecule 2-para-fluorophenylethanol has been investigated by combination of mass-analysed threshold-ionisation (MATI) spectroscopy and quantum chemistry ab initio density functional theory (DFT) calculations employing two different functionals: the B3LYP functional and the new hybrid functional M05. The MATI spectra measured via vibronic bands in the S1 intermediate state belonging to the most stable gauche conformer stabilised by an intramolecular OH...pi hydrogen bond are structureless, while the spectra recorded via bands of the anti conformer feature well-resolved peaks. This result is in a good accord with our theoretical predictions showing that upon ionisation, the anti conformer retains its structure, while the lowest-energy gauche conformer undergoes a significant structural change resulting in a break of the OH...pi bond. This and the good agreement between the measured band positions and the theoretically predicted frequencies for the cationic anti conformer confirm the conformational assignment. The result for the cation provides clear evidence for the existence of a nonclassical intramolecular OH...pi hydrogen bond if the electron density in the aromatic ring is sufficiently high as is the case only for the neutral molecule.

Research paper thumbnail of Water binding sites in 2-para- and 2-ortho-fluorophenylethanol: A high-resolution UV experiment and ab initio calculations

The singly hydrated complexes of the flexible prototype molecules 2-para-fluorophenylethanol and ... more The singly hydrated complexes of the flexible prototype molecules 2-para-fluorophenylethanol and 2-ortho-fluorophenylethanol have been investigated by combination of high-resolution resonance-enhanced two-photon ionization spectroscopy in a cold supersonic beam and quantum chemistry ab initio calculations. We have identified the conformational structures of the above complexes, which correspond to water binding to the most stable gauche monomer's conformers in both cases. No structural changes of the host molecules upon the attachment of a single water molecule have been found. For the 2-ortho-fluorophenylethanol-water complex we have observed an additional structure with one of the higher-in-energy gauche conformers of the monomer. This corroborates the assumption that the complexation with water stabilizes the higher-energy conformer of the monomer, precluding it from relaxation to the lowest-energy geometry.

Research paper thumbnail of An experimental toolbox for the generation of cold and ultracold polar molecules

Journal of Physics: Conference Series, 2017

Progress toward ultracold chemistry: ultracold atomic and photonic collisions Jesús Pérez-Ríos, M... more Progress toward ultracold chemistry: ultracold atomic and photonic collisions Jesús Pérez-Ríos, Maxence Lepers, Romain Vexiau et al. Thermodynamic of mixtures of ultracold Rydberg gases with different levels of excitation B V Zelener, S Y Bronin and A B Klyarfeld Nondestructive detection of polar molecules via Rydberg atoms M. Zeppenfeld Production and Detection of Ultracold Ground State 85Rb133Cs Molecules in the Lowest Vibrational Level by Short-Range Photoassociation

Research paper thumbnail of Identification of Conformational Structures of 2-Phenylethanol and Its Singly Hydrated Complex by Mass Selective High-Resolution Spectroscopy and ab Initio Calculations †

The Journal of Physical Chemistry A, 2008

The flexible prototype molecule 2-phenylethanol (2-PE) and its singly hydrated complex have been ... more The flexible prototype molecule 2-phenylethanol (2-PE) and its singly hydrated complex have been investigated in a cold supersonic beam by a combination of high-resolution two-color R2PI spectroscopy and quantum chemistry ab initio calculations. The existence of two monomer structures separated by a high potential energy barrier, gauche and anti ones, was proven. Higher energy conformers are supposed to relax to the observed ones during the jet expansion process. We have identified the conformational structure of the complex between 2-PE and water, which corresponds to water binding to the most stable gauche conformer. No detectable structural changes of the host 2-PE molecule have been observed upon attachment of a single water molecule. A conformational relaxation mechanism is suggested also for the 2-PE x H2O complex.

Research paper thumbnail of Fluorine substitution and nonconventional OH⋯π intramolecular bond: high-resolution UV spectroscopy and ab initio calculations of 2-(p-fluorophenyl)ethanol

Physical Chemistry Chemical Physics, 2008

The para-fluorinated flexible neurotransmitter analogue 2-phenylethanol has been investigated by ... more The para-fluorinated flexible neurotransmitter analogue 2-phenylethanol has been investigated by highly resolved resonance-enhanced two-photon ionisation two-colour UV laser spectroscopy with mass resolution and ab initio structural optimisations and energy calculations. Two stable conformations, gauche and anti, separated by a high potential barrier have been identified in the cold molecular beam by rotational analysis of the vibronic band structures. The theoretically predicted higher-lying conformations most likely relax to these two structures during the adiabatic expansion. The lowest-energy gauche conformer is stabilised by an intramolecular nonconventional OH...pi-type hydrogen bond between the terminal OH group of the side chain and the pi electrons of the phenyl ring. The good agreement between the experimental and theoretical results demonstrates that even the substitution with a strongly electronegative atom of 2-phenylethanol at the para position has no noticeable effect on the strength and orientation of the OH...pi bond.

Research paper thumbnail of Thermometry of Guided Molecular Beams from a Cryogenic Buffer-Gas Cell

ChemPhysChem, 2016

A comprehensive characterisation of cold molecular beams from a cryogenic buffer-gas cell, provid... more A comprehensive characterisation of cold molecular beams from a cryogenic buffer-gas cell, providing insight into the physics of buffer-gas cooling, is presented. Cold molecular beams are extracted from a cryogenic cell by electrostatic guiding, which is also used to measure their velocity distribution. The rotational-state distribution of the molecules is probed by radio-frequency resonant depletion spectroscopy. With the help of complete trajectory simulations, yielding the guiding efficiency for all of the thermally populated states, it is possible to determine both the rotational and the translational temperature of the molecules at the output of the buffer-gas cell. This thermometry method is demonstrated for various regimes of buffer-gas cooling and beam formation as well as for molecular species of different sizes (CH3 F and CF3 CCH). Comparison of the rotational and translational temperatures provides evidence of faster rotational thermalisation for the CH3 F/He system in the limit of low He density. In addition, the relaxation rates for different rotational states appear to be different.

Research paper thumbnail of Conformation Study of Ephedrine and 2-PHENYLETHANOL and Their Hydrated Clusters by Mass Selective High-Resolution Uv Spectroscopy and Ab Initio Calculations

A promising approach to the understanding of the interaction mechanisms and intrinsic properties ... more A promising approach to the understanding of the interaction mechanisms and intrinsic properties of biological systems is the spectroscopic investigation of their conformational structures and dynamics at molecular level in the gas phase. Recently we measured the first resonance-enhanced two-photon ionization (R2PI) spectra with rotational resolution (70 MHz FWHM laser bandwidth) and mass selection of almost all vibronic bands of the S

Research paper thumbnail of Continuous Centrifuge Decelerator for Polar Molecules

Physical Review Letters, 2014

Producing large samples of slow molecules from thermal-velocity ensembles is a formidable challen... more Producing large samples of slow molecules from thermal-velocity ensembles is a formidable challenge. Here we employ a centrifugal force to produce a continuous molecular beam with a high flux at near-zero velocities. We demonstrate deceleration of three electrically guided molecular species, CH 3 F, CF 3 H, and CF 3 CCH, with input velocities of up to 200 m s À1 to obtain beams with velocities below 15 m s À1 and intensities of several 10 9 mm À2 s À1. The centrifuge decelerator is easy to operate and can, in principle, slow down any guidable particle. It has the potential to become a standard technique for continuous deceleration of molecules.

Research paper thumbnail of High-Resolution Mass-Selective UV Spectroscopy of Pseudoephedrine: Evidence for Conformer-Specific Fragmentation

The Journal of Physical Chemistry A, 2011

Research paper thumbnail of genehmigten Dissertation

2. Univ.-Prof. Dr. Dr. h. c. A. Laubereau Die Dissertation wurde am 05.03.2007 bei der Technische... more 2. Univ.-Prof. Dr. Dr. h. c. A. Laubereau Die Dissertation wurde am 05.03.2007 bei der Technischen Universität München eingereicht und durch die Fakultät für Chemie am 29.03.2007 angenommen. 2 To the memory of my father,

Research paper thumbnail of Stopping intense beams of internally cold molecules via centrifugal forces

Bulletin of the American Physical Society, 2016

Research paper thumbnail of Investigation of Weak Intra- and Intermolecular Interactions and Conformational Structures of Flexible Molecules and Complexes by Mass Selective High Resolution Resonance Enhanced Two Photon Ionization Laser Spectroscopy

The goal of the work is to investigate intra- and intermolecular weak interactions and the subtle... more The goal of the work is to investigate intra- and intermolecular weak interactions and the subtle interplay between them, including hydrogen and dispersion bonds stabilizing conformeric structures of flexible molecules and small complexes. Accurate rotational constants and transition moment ratio are obtained by a combination of mass-selective rotationally resolved two-photon two-color resonance-enhanced ionization spectroscopy of cold molecular beams, rotational spectra fitting technique based on genetic algorithms, and high-level quantum chemistry ab initio calculations. The studied model species include two groups: i) complexes of water, acetylene, and argon with a molecule pertaining two conjugated π-electron systems, leading to a strong electron density delocalization: styrene and its fluorinated derivative; and ii) the flexible biologically relevant molecule 2-phenylethanol and its complex with argon, and the neurotransmitter ephedrine. The assigned gauche structure of 2-pheny...

Research paper thumbnail of A Road Map to Ultracold Polyatomic Molecules

Research paper thumbnail of Internal-state thermometry of cold polyatomic molecules

Bulletin of the American Physical Society, 2016

Research paper thumbnail of A Centrifuge Decelerator: Slowing down Continuous Beams of Polar Molecules by an Inertial Force

Bulletin of the American Physical Society, 2013

Research paper thumbnail of Electrically guided continuous supersonic beams of polar molecules from a cryogenic buffer-gas source

Bulletin of the American Physical Society, 2012

Submitted for the DAMOP12 Meeting of The American Physical Society Electrically guided continuous... more Submitted for the DAMOP12 Meeting of The American Physical Society Electrically guided continuous supersonic beams of polar molecules from a cryogenic buffer-gas source XING WU, CHRISTIAN SOMMER, SOTIR CHERVENKOV, ANDREAS ROHLFES, MARTIN ZEPPENFELD, LAURENS VAN BUUREN, GERHARD REMPE, Max-Planck-Institut für Quantenoptik — In order to obtain dense samples of internally and translationally cold polar molecules, we use the method of buffer-gas cooling [1], combined with supersonic expansion. We have demonstrated that when the cryogenic buffer-gas cell is operated in a supersonic regime, molecular fluxes are hydrodynamically enhanced by up to two orders of magnitude. Meanwhile, the translational velocity profile of the output molecular beam is cooled to beyond Mach number 6 via supersonic expansion. Due to the cryogenic cell temperature, the forward velocity of the supersonic molecular beam is below 190m/s. The low-field-seeking molecules in the so-produced continuous supersonic beam ar...

Research paper thumbnail of A high density source of cold, slow and rotationally pure polar molecules

Research paper thumbnail of Observation of cold dipolar collisions between centrifuge decelerated molecules

Research paper thumbnail of A cryofuge for cold-collision experiments with slow polar molecules

Science (New York, N.Y.), Jan 3, 2017

Ultracold molecules represent a fascinating research frontier in physics and chemistry, but it ha... more Ultracold molecules represent a fascinating research frontier in physics and chemistry, but it has proven challenging to prepare dense samples at low velocities. Here, we present a solution to this goal by means of a nonconventional approach dubbed cryofuge. It uses centrifugal force to bring cryogenically cooled molecules to kinetic energies below 1 K × kB in the laboratory frame, where kB is the Boltzmann constant, with corresponding fluxes exceeding 1010 per second at velocities below 20 meters per second. By attaining densities higher than 109 per cubic centimeter and interaction times longer than 25 milliseconds in samples of fluoromethane as well as deuterated ammonia, we observed cold dipolar collisions between molecules and determined their collision cross sections.

Research paper thumbnail of Back Cover: Thermometry of Guided Molecular Beams from a Cryogenic Buffer-Gas Cell (ChemPhysChem 22/2016)

Research paper thumbnail of Mass analysed threshold ionisation spectroscopy of flexible 2-para-fluorophenylethanol conformers with and without an intramolecular OH⋯π bond

Physical Chemistry Chemical Physics, 2009

The cationic state of the prototype flexible molecule 2-para-fluorophenylethanol has been investi... more The cationic state of the prototype flexible molecule 2-para-fluorophenylethanol has been investigated by combination of mass-analysed threshold-ionisation (MATI) spectroscopy and quantum chemistry ab initio density functional theory (DFT) calculations employing two different functionals: the B3LYP functional and the new hybrid functional M05. The MATI spectra measured via vibronic bands in the S1 intermediate state belonging to the most stable gauche conformer stabilised by an intramolecular OH...pi hydrogen bond are structureless, while the spectra recorded via bands of the anti conformer feature well-resolved peaks. This result is in a good accord with our theoretical predictions showing that upon ionisation, the anti conformer retains its structure, while the lowest-energy gauche conformer undergoes a significant structural change resulting in a break of the OH...pi bond. This and the good agreement between the measured band positions and the theoretically predicted frequencies for the cationic anti conformer confirm the conformational assignment. The result for the cation provides clear evidence for the existence of a nonclassical intramolecular OH...pi hydrogen bond if the electron density in the aromatic ring is sufficiently high as is the case only for the neutral molecule.

Research paper thumbnail of Water binding sites in 2-para- and 2-ortho-fluorophenylethanol: A high-resolution UV experiment and ab initio calculations

The singly hydrated complexes of the flexible prototype molecules 2-para-fluorophenylethanol and ... more The singly hydrated complexes of the flexible prototype molecules 2-para-fluorophenylethanol and 2-ortho-fluorophenylethanol have been investigated by combination of high-resolution resonance-enhanced two-photon ionization spectroscopy in a cold supersonic beam and quantum chemistry ab initio calculations. We have identified the conformational structures of the above complexes, which correspond to water binding to the most stable gauche monomer's conformers in both cases. No structural changes of the host molecules upon the attachment of a single water molecule have been found. For the 2-ortho-fluorophenylethanol-water complex we have observed an additional structure with one of the higher-in-energy gauche conformers of the monomer. This corroborates the assumption that the complexation with water stabilizes the higher-energy conformer of the monomer, precluding it from relaxation to the lowest-energy geometry.

Research paper thumbnail of An experimental toolbox for the generation of cold and ultracold polar molecules

Journal of Physics: Conference Series, 2017

Progress toward ultracold chemistry: ultracold atomic and photonic collisions Jesús Pérez-Ríos, M... more Progress toward ultracold chemistry: ultracold atomic and photonic collisions Jesús Pérez-Ríos, Maxence Lepers, Romain Vexiau et al. Thermodynamic of mixtures of ultracold Rydberg gases with different levels of excitation B V Zelener, S Y Bronin and A B Klyarfeld Nondestructive detection of polar molecules via Rydberg atoms M. Zeppenfeld Production and Detection of Ultracold Ground State 85Rb133Cs Molecules in the Lowest Vibrational Level by Short-Range Photoassociation

Research paper thumbnail of Identification of Conformational Structures of 2-Phenylethanol and Its Singly Hydrated Complex by Mass Selective High-Resolution Spectroscopy and ab Initio Calculations †

The Journal of Physical Chemistry A, 2008

The flexible prototype molecule 2-phenylethanol (2-PE) and its singly hydrated complex have been ... more The flexible prototype molecule 2-phenylethanol (2-PE) and its singly hydrated complex have been investigated in a cold supersonic beam by a combination of high-resolution two-color R2PI spectroscopy and quantum chemistry ab initio calculations. The existence of two monomer structures separated by a high potential energy barrier, gauche and anti ones, was proven. Higher energy conformers are supposed to relax to the observed ones during the jet expansion process. We have identified the conformational structure of the complex between 2-PE and water, which corresponds to water binding to the most stable gauche conformer. No detectable structural changes of the host 2-PE molecule have been observed upon attachment of a single water molecule. A conformational relaxation mechanism is suggested also for the 2-PE x H2O complex.

Research paper thumbnail of Fluorine substitution and nonconventional OH⋯π intramolecular bond: high-resolution UV spectroscopy and ab initio calculations of 2-(p-fluorophenyl)ethanol

Physical Chemistry Chemical Physics, 2008

The para-fluorinated flexible neurotransmitter analogue 2-phenylethanol has been investigated by ... more The para-fluorinated flexible neurotransmitter analogue 2-phenylethanol has been investigated by highly resolved resonance-enhanced two-photon ionisation two-colour UV laser spectroscopy with mass resolution and ab initio structural optimisations and energy calculations. Two stable conformations, gauche and anti, separated by a high potential barrier have been identified in the cold molecular beam by rotational analysis of the vibronic band structures. The theoretically predicted higher-lying conformations most likely relax to these two structures during the adiabatic expansion. The lowest-energy gauche conformer is stabilised by an intramolecular nonconventional OH...pi-type hydrogen bond between the terminal OH group of the side chain and the pi electrons of the phenyl ring. The good agreement between the experimental and theoretical results demonstrates that even the substitution with a strongly electronegative atom of 2-phenylethanol at the para position has no noticeable effect on the strength and orientation of the OH...pi bond.

Research paper thumbnail of Thermometry of Guided Molecular Beams from a Cryogenic Buffer-Gas Cell

ChemPhysChem, 2016

A comprehensive characterisation of cold molecular beams from a cryogenic buffer-gas cell, provid... more A comprehensive characterisation of cold molecular beams from a cryogenic buffer-gas cell, providing insight into the physics of buffer-gas cooling, is presented. Cold molecular beams are extracted from a cryogenic cell by electrostatic guiding, which is also used to measure their velocity distribution. The rotational-state distribution of the molecules is probed by radio-frequency resonant depletion spectroscopy. With the help of complete trajectory simulations, yielding the guiding efficiency for all of the thermally populated states, it is possible to determine both the rotational and the translational temperature of the molecules at the output of the buffer-gas cell. This thermometry method is demonstrated for various regimes of buffer-gas cooling and beam formation as well as for molecular species of different sizes (CH3 F and CF3 CCH). Comparison of the rotational and translational temperatures provides evidence of faster rotational thermalisation for the CH3 F/He system in the limit of low He density. In addition, the relaxation rates for different rotational states appear to be different.