Sarantos Marinakis | University of Patras (original) (raw)

Papers by Sarantos Marinakis

Monthly Notices of the Royal Astronomical Society, Jan 15, 2020

To understand how phosphorus (P)-bearing molecules are formed in star-forming regions, we have an... more To understand how phosphorus (P)-bearing molecules are formed in star-forming regions, we have analysed the Atacama Large Millimeter/Submillimeter Array (ALMA) observations of PN and PO towards the massive star-forming region AFGL 5142, combined with a new analysis of the data of the comet 67P/Churyumov-Gerasimenko taken with the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument onboard Rosetta. The ALMA maps show that the emission of PN and PO arises from several spots associated with lowvelocity gas with narrow linewidths in the cavity walls of a bipolar outflow. PO is more abundant than PN in most of the spots, with the PO/PN ratio increasing as a function of the distance to the protostar. Our data favour a formation scenario in which shocks sputter phosphorus from the surface of dust grains, and gas-phase photochemistry induced by UV photons from the protostar allows efficient formation of the two species in the cavity walls. Our analysis of the ROSINA data has revealed that PO is the main carrier of P in the comet, with PO/PN > 10. Since comets may have delivered a significant amount of prebiotic material to the early Earth, this finding suggests that PO could contribute significantly to the phosphorus reservoir during the dawn of our planet. There is evidence that PO was already in the cometary ices prior to the birth of the Sun, so the chemical budget of the comet might be inherited from the natal environment of the Solar system, which is thought to be a stellar cluster including also massive stars.

Journal of Chemical Physics, Jan 19, 2021

Rotational excitation of interstellar PN molecules induced by collisions with H 2 is investigated... more Rotational excitation of interstellar PN molecules induced by collisions with H 2 is investigated. We present the first ab initio four-dimensional potential energy surface (PES) for the PN-H 2 van der Waals system. The PES was obtained using an explicitly-correlated coupled cluster approach with single, double, and perturbative triple excitations [CCSD(T)-F12b]. The method of interpolating moving least squares was used to construct an analytical PES from these data. The equilibrium structure of the complex was found to be linear, with the H 2 aligned at the N end of the PN molecule, at an intermolecular separation of 4.2 Å. The corresponding well-depth is 224.3 cm −1. The dissociation energies were found to be 40.19 cm −1 and 75.05 cm −1 for complexes of PN with ortho-H 2 and para-H 2 , respectively. Integral cross-sections for rotational excitation in PN-H 2 collisions were calculated using the new PES, and were found to be strongly dependent on the rotational level of the H 2 molecule. These new collisional data will be crucial to improve the estimation of PN abundance in the interstellar medium from observational spectra.

Journal of Chemical Physics, Dec 1, 2004

The product state-resolved dynamics of the reactions H+H2O/D2O→OH/OD(2ΠΩ;v′,N′,f )+H2/HD have bee... more The product state-resolved dynamics of the reactions H+H2O/D2O→OH/OD(2ΠΩ;v′,N′,f )+H2/HD have been explored at center-of-mass collision energies around 1.2, 1.4, and 2.5 eV. The experiments employ pulsed laser photolysis coupled with polarized Doppler-resolved laser induced fluorescence detection of the OH/OD radical products. The populations in the OH spin–orbit states at a collision energy of 1.2 eV have been determined for the H+H2O reaction, and for low rotational levels they are shown to deviate from the statistical limit. For the H+D2O reaction at the highest collision energy studied the OD(2Π3/2,v′=0,N′=1,A′) angular distributions show scattering over a wide range of angles with a preference towards the forward direction. The kinetic energy release distributions obtained at 2.5 eV also indicate that the HD coproducts are born with significantly more internal excitation than at 1.4 eV. The OD(2Π3/2,v′=0,N′=1,A′) angular and kinetic energy release distributions are almost identical to those of their spin–orbit excited OD(2Π1/2,v′=0,N′=1,A′) counterpart. The data are compared with previous experimental measurements at similar collision energies, and with the results of previously published quasiclassical trajectory and quantum mechanical calculations employing the most recently developed potential energy surface. Product OH/OD spin–orbit effects in the reaction are discussed with reference to simple models.

Journal of Chemical Physics, Jan 26, 2009

Zeeman quantum beat spectroscopy has been used to measure the 300 K rate constants for the angula... more Zeeman quantum beat spectroscopy has been used to measure the 300 K rate constants for the angular momentum depolarization of OH͑A 2 ⌺ + ͒ in the presence of Ar. We show that the beat amplitude at short times, in the absence of collisions, is well described by previously developed line strength theory for ͑1+1͒ laser induced fluorescence. The subsequent pressure dependent decay of the beat amplitude is used to extract depolarization rate constants and estimates of collisional depolarization cross sections. Depolarization accompanies both inelastic collisions, giving rise to rotational energy transfer, and elastic collisions, which change m j but conserve j. Previous experimental studies, as well as classical theory, suggest that elastic scattering contributes around 20% to the observed total depolarization rate at low j. Simulation of the experimental beat amplitudes, using theoretical calculations presented in the preceding paper, reveals that depolarization of OH͑A͒ by Ar has a rate constant comparable to, if not larger than, that for energy transfer. This is consistent with a significant tilting or realignment of jЈ away from j on collision. The experimental data are used to provide a detailed test of quantum mechanical and quasiclassical trajectory scattering calculations performed on a recently developed ab initio potential energy surface of Kłos et al. ͓J. Chem. Phys. 129, 054301 ͑2008͔͒. The calculations and simulations account well for the observed cross sections at high N, but underestimate the experimental results by between 10% and 20% at low N, possibly due to remaining inaccuracies in the potential energy surface or perhaps to limitations in the dynamical approximations made, particularly the freezing of the OH͑A͒ bond.

Acta Crystallographica Section E: Crystallographic Communications, Mar 18, 2015

The asymmetric unit of the title complex, [NiBr(NO)-{P(C 6 H 5) 3 } 2 ], comprises two independen... more The asymmetric unit of the title complex, [NiBr(NO)-{P(C 6 H 5) 3 } 2 ], comprises two independent molecules each with a similar configuration. The Ni II cation is coordinated by one bromide anion, one nitrosyl anion and two triphenylphosphane molecules in a distorted BrNP 2 tetrahedral coordination geometry. The coordination of the nitrosyl group is non-linear, the Ni-NO angles being 150.2 (5) and 151.2 (5) in the two independent molecules. In the crystal, molecules are linked by weak C-HÁ Á ÁBr hydrogen bonds and weak C-HÁ Á Á interactions into a three-dimensional supramolecular architecture.

Journal of Molecular Liquids, Sep 1, 2019

The microscopic structure of Ar-N 2 supercritical mixtures was obtained using neutron scattering ... more The microscopic structure of Ar-N 2 supercritical mixtures was obtained using neutron scattering experiments at temperatures between 128.4-154.1

Journal of Molecular Liquids, Nov 1, 2017

Thermodynamics, microscopic structure and (single molecule and collective) dynamics in Xe-N 2 sup... more Thermodynamics, microscopic structure and (single molecule and collective) dynamics in Xe-N 2 supercritical mixtures were studied using Molecular Dynamics simulations at a temperature of T = 323 K. The results agree well with previous experimental work on PVT-data and depolarized Rayleigh light scattering (DRLS). By using the corresponding DRLS time-correlation functions (TCFs), the contribution of orientational, interaction-induced and cross terms in the total DRLS TCF were evaluated. At all densities studied, the orientational part was found to be the most dominant. The Molecular Dynamics interaction potential model was compared with the most recent ab initio interaction potential energy surface (PES). Furthermore, quantum mechanical scattering calculations on the ab initio PES were used to provide integral and differential cross sections.

Journal of Supercritical Fluids, May 1, 2005

The molecular dynamics (MD) simulation technique has been employed to investigate the self-diffus... more The molecular dynamics (MD) simulation technique has been employed to investigate the self-diffusion coefficients of neat liquid and supercritical (SC) Xenon over a wide range of thermodynamic conditions. The fluid has been studied at densities in the range 0.0700-3.2141 g/cm 3 and temperatures from 203 to 343 K. The simulations were based on a pair-wise additive potential model with ε/k B = 212 K and σ = 0.3905 nm, which is presented for the first time here. The self-diffusion coefficients obtained are shown to be in good agreement with experimental values reported by Prins and coworkers [P.W.E. Peereboom, H. Luigjes, K.O. Prins, An NMR Spin-echo study of self-diffusion in Xenon, Physica A 156 (1989) 260], covering PVT data up to 1500 bar. Theoretical results for self-diffusion coefficients from various theoretical and empirical models are tested against experimental and MD results. In addition, the structure of the fluid is presented in terms of the pair distribution functions and possible correlation of its local behaviour with diffusivity is briefly discussed.

Physical Chemistry Chemical Physics, 2009

... Π) + Xe collisions. Grant Patersona, Sarandis Marinakisa, Jacek Kłosb, Matthew L. Costena an... more ... Π) + Xe collisions. Grant Patersona, Sarandis Marinakisa, Jacek Kłosb, Matthew L. Costena and Kenneth G. McKendrick*a. a School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, UK EH14 4AS. ...

Molecular Physics, Jul 1, 2005

The depolarization of the rotational angular momentum of electronically excited OH(2 AE) radicals... more The depolarization of the rotational angular momentum of electronically excited OH(2 AE) radicals through collisions with water molecules has been measured using Zeeman quantum beat spectroscopy. The new data have permitted the evaluation of OH(A) state-specific quenching and angular momentum depolarization cross-sections for superthermal OH(A) radicals with mean relative velocities centred around 3500 m s À1. The quenching cross-sections are compared both with values available in the literature, and with predictions based on a simple harpoon model, and are found to be in good qualitative accord with previous findings. For the lowest rotational levels studied, the depolarization cross-sections (which include contributions from both elastic and inelastic processes in OH(A)) are found to approach s100 Å 2 , only slightly below the high-temperature cross-sections for rotational energy transfer determined elsewhere. The data suggest that under the present conditions rotational energy transfer is accompanied by significant depolarization. The cross-section for the translational moderation of superthermal OH(X) by water is also determined in the present study.

Physical Chemistry Chemical Physics, 2007

One-colour polarization spectroscopy (PS) on the OH A (2)Sigma(+)- X (2)Pi(0,0) band has been use... more One-colour polarization spectroscopy (PS) on the OH A (2)Sigma(+)- X (2)Pi(0,0) band has been used to measure the removal of bulk rotational angular momentum alignment of ground-state OH(X (2)Pi) in collisions with He and Ar. Pseudo-first-order PS signal decays at different collider partial pressures were used to determine second-order decay rate constants for the X (2)Pi(3/2), J = 1.5-6.5, e states. The PS signal decay rate constant, k(PS), is sensitive to all processes that remove population and destroy polarization. The contribution to k(PS) from pure (elastic) alignment depolarization within the initial level, k(DEP), can be extracted by subtracting the independently measured or predicted sum of the rate constants for total rotational energy transfer (RET), k(RET), and for Lambda-doublet changing, k(Lambda), collisions from k(PS). Literature values of k(RET) and k(Lambda) are available from experiments with He and Ar, and from quantum scattering calculations for Ar only. We therefore also present the results of new, exact, fully quantum mechanical calculations of k(RET) and k(Lambda) on the most recent ab initio OH(X)-He potential energy surface of Lee et al. [J. Chem. Phys. 2000, 113, 5736]. The results for k(DEP) from this subtraction for He are found to be modest, around 0.4 x 10(-10) cm(3) s(-1), whereas for Ar k(DEP) is found to range between 0.6 +/- 0.2 x 10(-10) cm(3) s(-1) and 1.7 +/- 0.3 x 10(-10) cm(3) s(-1), comparable to total population removal rate constants. The differences between k(DEP) for the two colliders are most likely explained by the presence of a substantially deeper attractive well for Ar than for He. The measurement of k(DEP) may provide a useful new tool that is more sensitive to the form of the long-range part of the intermolecular potential than rotational state-changing collisions.

Chemical Society Reviews, 2008

This tutorial review examines the proposition that vector properties reveal more about the underl... more This tutorial review examines the proposition that vector properties reveal more about the underlying potential energy surfaces controlling the inelastic exchange of energy in intermolecular collisions than conventional scalar measurements. Exciting recent experimental progress is summarized in the form of six selected cases studies. The new information that has been extracted is compared with the predictions of complementary theory. Likely future prospects and promising avenues for further progress are discussed. The treatment should appeal to all those with interests in the forces governing intermolecular interactions, especially in gas-phase collisions.

Journal of Physical Chemistry B, Nov 18, 2022

Chemical Physics Letters, Aug 1, 2011

Quantum mechanical (QM) close-coupling calculations have been used to study fully quantum statere... more Quantum mechanical (QM) close-coupling calculations have been used to study fully quantum stateresolved product differential rotational alignment in collisions of NO(X 2 P 1/2 , v = 0, j = 0.5, f) + Kr at a collision energy of 500 cm À1 , using the most recent ab initio potential energy surface of Wen et al. [12]. We show that fully quantum state-resolved differential alignment exhibits a noticeable paritydependent behavior. The results are discussed and compared with previous experimental and theoretical studies on NO(X) + He/Ar inelastic scattering at similar collision energies.

Astronomy and Astrophysics, Sep 1, 2019

Context. Because of their high reactivity, the CH and OH radicals are of particular interest in a... more Context. Because of their high reactivity, the CH and OH radicals are of particular interest in astrochemistry. Modeling of CH and OH molecules requires the calculation of accurate radiative Einstein coefficients and rate coefficients for (de)excitation by collisions with the most abundant species such as H 2 and He. Aims. The present paper focuses on the calculation of inelastic rate coefficients among the lowest OH/CH hyperfine levels in their ground vibrational state induced by collisions with He atoms. Methods. Calculations of hyperfine (de)excitation of CH/OH by He were performed using the close-coupling and recoupling methods from the most recent ab initio potential energy surfaces. Results. Cross sections for transitions among the 60 and 56 lowest hyperfine levels of CH and OH, respectively, were calculated for collision energies up to 2500 cm −1. These cross-sections were used to calculate the rate coefficients for temperatures between 10 and 300 K. A propensity rule for transitions with ∆F = ∆ j was observed. Conclusions. The new rate coefficients will help significantly in interpreting the CH/OH spectroscopic data observed with current and future telescopes, and help to accurately describe the OH masers and the hyperfine anomalies in CH emission spectra.

Physical Chemistry Chemical Physics, 2004

ABSTRACT Absolute values of the cross-section for the abstraction reaction between fast H atoms a... more ABSTRACT Absolute values of the cross-section for the abstraction reaction between fast H atoms and D2O have been determined experimentally at mean collision energies of 1.83 eV and 2.48 eV. The data support the value for the cross-section recently reported for the H + H2O reaction at 2.46 eV, which was significantly lower than previous measurements. The measurements employ the photodissociation of water as a calibrant for OH(OD) concentration. The OH rotational quantum state population distributions for the fully protonated reaction, as well as those for the photodissociation of water, are shown to be in good agreement with previous work. The measurements are compared with new quasi-classical trajectory calculations and published quantum mechanical scattering calculations using the most recently developed potential energy surface.

Physical review, May 12, 2020

Physics of supercritical state is understood to a much lesser degree compared to subcritical liqu... more Physics of supercritical state is understood to a much lesser degree compared to subcritical liquids. Carbon dioxide in particular has been intensely studied, yet little is known about the supercritical part of its phase diagram. Here, we combine neutron scattering experiments and molecular dynamics simulations and demonstrate the structural crossover at the Frenkel line. The crossover is seen at pressures as high as 14 times the critical pressure and is evidenced by changes of the main features of the structure factor and pair distribution functions. Usage: Secondary publications and information retrieval purposes.

Nature Chemistry, Oct 28, 2012

The hydroxyl radical (OH) is one of the most interesting molecules in molecular dynamics. In part... more The hydroxyl radical (OH) is one of the most interesting molecules in molecular dynamics. In particular, inelastic collisions of free radicals such as OH are profoundly important in environments ranging from combustion to astrochemistry. However, measuring the velocities of OH molecules in specific internal quantum states has proven to be very difficult. A method that can provide this important information is velocity-map imaging. Although this technique is very widely applicable in principle, it does require a sensitive and selective laser-ionization scheme. Here we show that, under the right conditions, velocity-map imaging can be applied to the study of the inelastic scattering of OH using crossed-molecular-beam methods. We measure fully quantum-state-specified product angular distributions for OH collisions with helium and argon. The agreement between exact close-coupling quantum scattering calculations on ab initio potential energy surfaces and experimental data is generally very satisfactory, except for scattering in the most forward directions.

Journal of Chemical Physics, Dec 17, 2012