Piergiorgio Casavecchia

• Prof. of Physical Chemistry
• University of Perugia

The inelastic and reactive scattering dynamics of O(3P) atoms on a 6H-silicon carbide (SiC) surface were investigated as a function of temperature with a molecular beamsurface scattering technique that employed a rotatable mass spectrometer detector. One set of experiments used a pulsed hyperthermal beam that produced ∼8 km s−1 O atoms, and another...

The theoretical investigation of large aromatic compounds interacting with atomic oxygen is a computationally very challenging problem for the requirements in terms of computer time and scratch disk space. The use of very accurate methods like the CCSD(T) with very extended basis sets is unfeasible. It is necessary to use less expensive methods. In...

Despite the relevance of the reactions of the prototypical nitrogen-containing sixmembered aromatic molecule (N-heterocyclic) of pyridine (C6H5N) in environmental science, astrochemistry, planetary science, prebiotic chemistry, and material science, few experimental/theoretical studies exist on the bimolecular reactions involving pyridine and neutr...

Despite extensive experimental and theoretical studies on the kinetics of the O(3P) + C7H8 (toluene) reaction and a pioneering crossed molecular beam (CMB) investigation, the branching fractions (BFs) of the...

In this contribution, dedicated to the memory of Prof. Gian Gualberto Volpi, we provide a short review of recent work carried out in our laboratory on reactive scattering studies of the reaction dynamics of atomic oxygen with nitrogen-bearing organic molecules. Specifically, we focus on the polyatomic bimolecular reactions of atomic oxygen, both in...

Acrylonitrile (CH2CHCN) is ubiquitous in space (molecular clouds, solar-type protostars, circumstellar envelopes) and is also abundant in the upper atmosphere of Titan and in comets. The reaction O(3P) + CH2CHCN...

In this contribution, we will present a computational study of the reactions involving N(2D) and simple aromatic hydrocarbons, like benzene or toluene. The aim is to determine the chemical reactivity of N(2D) with aromatic species after previous investigations with aliphatic molecules, in order to establish which level of calculation is necessary t...

We report on a combined experimental and theoretical investigation of the N(2D) + C6H6 (benzene) reaction, which is of relevance in the aromatic chemistry of the atmosphere of Titan. Experimentally, the reaction was studied (i) under single-collision conditions by the crossed molecular beams (CMB) scattering method with mass spectrometric detection...

The reaction between the ground-state hydroxyl radical, OH(2Π), and ethylene, C2H4, has been investigated under single-collision conditions by the crossed molecular beam scattering technique with mass-spectrometric detection and time-of-flight analysis at the collision energy of 50.4 kJ/mol. Electronic structure calculations of the underlying poten...

Cyanoacetylene (HCCCN), the first member of the cyanopolyyne family (HCnN, where n = 3, 5, 7, ...), is of particular interest in astrochemistry being ubiquitous in space (molecular clouds, solar-type protostars, protoplanetary disks, circumstellar envelopes, and external galaxies) and also relatively abundant. It is also abundant in the upper atmos...

Two quantum effects can enable reactions to take place at energies below the barrier separating reactants from products: tunnelling and intersystem crossing between coupled potential energy surfaces. Here we show that intersystem crossing in the region between the pre-reactive complex and the reaction barrier can control the rate of bimolecular rea...

We report on a combined experimental and theoretical investigation of the N(2D) + CH2CCH2 (allene) reaction of relevance in the atmospheric chemistry of Titan. Experimentally, the reaction was investigated (i) under single-collision conditions by the crossed molecular beams (CMB) scattering method with mass spectrometric detection and time-of-fligh...

The reaction of electronically excited nitrogen atoms, N(2D), with vinyl cyanide, CH2CHCN, has been investigated under single-collision conditions by the crossed molecular beam (CMB) scattering method with mass spectrometric detection and time-of-flight (TOF) analysis at the collision energy, Ec, of 31.4 kJ/mol. Synergistic electronic structure cal...

The interaction between oxygen atoms in their first electronically excited state 1D with toluene has been characterized by electronic structure calculations. We focused our attention, in particular, on the different pathways leading to the formation of CO. Six different reaction channels have been investigated. Our results suggest that, while for a...

Atomic oxygen reactions can contribute significantly to the oxidation of unsaturated aliphatic and aromatic hydrocarbons. The reaction mechanism is started by electrophilic O atom addition to the unsaturated bond(s) to form "chemically activated" triplet oxy-intermediate(s), which can evolve adiabatically on the triplet potential energy surface (PE...

The reaction between cyano radicals (CN, X2Σ+) and cyanoethene (C2H3CN) has been investigated by a combined approach coupling crossed molecular beam (CMB) experiments with mass spectrometric detection and time-of-flight analysis at a collision energy of 44.6 kJ mol-1 and electronic structure calculations to determine the relevant potential energy s...

The reaction of excited nitrogen atoms N(2D) with CH3CCH (methylacetylene) was investigated under single-collision conditions by the crossed molecular beams (CMB) scattering method with mass spectrometric detection and time-of-flight analysis at the collision energy (Ec) of 31.0 kJ/mol. Synergistic electronic structure calculations of the doublet p...

Reliable modeling of hydrocarbon oxidation relies critically on knowledge of the branching fractions (BFs) as a function of temperature (T) and pressure (p) for the products of the reaction of the hydrocarbon with atomic oxygen in its ground state, O(³P). During the past decade, we have performed in-depth investigations of the reactions of O(³P) wi...

The interaction between nitrogen atoms in their first electronically excited state ²D and oxygen atoms in their ground state ³P or in the first electronically excited state ¹D with toluene has been characterized by electronic structure calculations. We focused our attention, in particular, on the different sites of attack of nitrogen or oxygen to t...

The reaction of the nitrogen atom (N) in its first electronically excited state (²D) with cyanoacetylene (HC3N) has been investigated under single-collision conditions by using the crossed molecular beam method with mass spectrometric detection at a collision energy of 31 kJ mol⁻¹. With the support of electronic structure calculations, we found tha...

Pyridine is a heterocyclic aromatic molecule of gross formula C5H5N with a six-membered ring similar to the structure of benzene where one CH group of the ring is replaced by a nitrogen atom. The molecule itself is not abundant in nature, but its derivatives are often part of important biomolecules. For instance, it is one of the basic units in the...

The reactivity of the prototypical aromatic six-membered N-heterocyclic pyridine is of relevance in atmospheric/combustion chemistry, as well as astrochemistry and prebiotic chemistry. Yet, experimental/theoretical studies of elementary reactions involving pyridine are scarce, with little information on primary reaction products and their branching...

In combustion, the overall chemical changeover is the result of an intricate network of elementary reactions (unimolecular, bimolecular and termolecular) which are classified according to their role (initiation, propagation, branching, termination steps) in the chain reaction. To implement a realistic combustion model, a deep knowledge of the chemi...

The extent of intersystem crossing in the O(3P) + C6H6 reaction, a prototypical system for spin-forbidden reactions in oxygenated aromatic molecules, is theoretically evaluated for the first time. Calculations are performed using nonadiabatic transition-state theory coupled with stochastic master equation simulations and Landau-Zener theory. It is...

The reactions between nitrogen atoms in their first electronically excited state 2D with benzene and toluene have been characterized by electronic structure calculations of the stationary points along the minimum energy path. We focused our attention, in particular, to the channels leading to the imidogen radical for the first reaction implying the...

Molecular beam-surface scattering experiments were used to obtain fundamental data on gas-surface interactions that are central to the ablation of carbon during hypersonic flight through air. Continuous beams containing O or N atoms with incident velocities of ∼2000 m s⁻¹ were directed at a vitreous carbon surface at temperatures in the range, 800–...

The reaction of ground state atomic oxygen with terminal alkenes plays an important role in both atmospheric and combustion chemistry. Because of its complicated nature, which involves intersystem crossing from the triplet to the singlet potential energy surface, its channel specific reactivity has been explored only for a few species in restricted...

Information on the detailed mechanism and dynamics (primary products, branching fractions (BFs), and channel specific rate constants as a function of temperature) for many important combustion reactions of O(³P) with unsaturated hydrocarbons is still lacking. We report synergistic experimental/theoretical studies on the mechanism and dynamics of th...

The identification of the primary products and the determination of their branching ratios as a function of translational energy (temperature) for multi-channel elementary (bimolecular) reactions of importance in combustion flames and plasma-assisted combustion still represent a challenge for traditional kinetics experiments. On the other hand, thi...

Understanding the oxidation mechanisms of heat shields is key to the reliable design of hypersonic vehicles. We have been using molecular beam-surface scattering experiments to gain an understanding of the high temperature oxidation of carbon-based materials.[1-4] SiC is a model for high-temperature ceramic materials that are considered for use on...

The reaction between nitrogen atoms in their first electronically excited state ²D with benzene has been characterized by electronic structure calculations of the stationary points along the minimum energy path. We focused our attention, in particular, to the two channels leading to C6H5N (phenylnitrene) + H and C5H5N (pyridine) + CH, due to the re...

Detailed understanding of the mechanism of the combustion relevant multichannel reactions of O(³P) with unsaturated hydrocarbons (UHs) requires the identification of all primary reaction products, the determination of their branching ratios and assessment of intersystem crossing (ISC) between triplet and singlet potential energy surfaces (PESs). Th...

The reaction between nitrogen atoms in their first electronically excited state ²D with benzene has been characterized by electronic structure calculations of the stationary points along the minimum energy path. According to this study, there are six open channels leading to C6H5N (phenylnitrene) + H, C6H4 + NH2, C5H5 (cyclopentadienyl) + HNC, C5H5...

The synthesis of nitrogen-containing organic molecules is a crucial step in prebiotic chemistry, as they are potential precursors of important biological molecules such as nucleobases and amino acids. In this respect, unsaturated species like nitriles (containing a –CN group) or imines (containing a carbon–nitrogen double bond) are particularly int...

Accurate measurements of product state-resolved angular distributions are central to fundamental studies of chemical reaction dynamics. Yet, fine quantum-mechanical structures in product angular distributions of a reactive scattering process, such as the fast oscillations in the forward-scattering direction, have never been observed experimentally...

A combined experimental/theoretical study is performed to advance our understanding of the dynamics of the prototypical tetra-atom, complex-forming reaction OH + CO→ H + CO2, which is also of great practical relevance in combustion, Earth atmosphere and, potentially, Mars’ atmosphere and interstellar chemistry. New crossed molecular beam experiment...

The observation of hydrogen peroxide in the interstellar medium represents a remarkable discovery for the astrochemistry community. The prototypical role that this molecule, arguably the simplest chiral molecule, plays in the evolution of life in biospheres, is related to the chirality change transitions associated with the torsional motions around...

This review summarizes the developments in polyatomic reaction dynamics, focusing on reactions of unsaturated hydrocarbons with O-atoms and methane with atoms/radicals.

The recent observation of propylene oxide in the interstellar medium has raised unusually large interest in view of the prototypical role that this molecule plays in chemical and biophysical investigations of chirality, a phenomenon that transversely pervades modern science for implications ranging from the mechanism of the origin and early evoluti...

We report preliminary combined experimental/theoretical results on O(³P)+1-butene reaction dynamics with focus on atomic hydrogen displacement and molecular hydrogen elimination channels. Dynamics and relative yield of the ethylvinoxy+H and ethylketene+H2 product channels are characterized in crossed beam experiments. Stationary points and energeti...

We have performed synergic experimental/theoretical studies on the mechanism of the O(3P)+CH3CCH (propyne) reaction by combining crossed molecular beams (CMB) experiments with mass-spectrometric detection and time-of-flight analysis at 9.2 kcal/mol collision energy (Ec) with ab initio electronic structure calculations at a high-level of theory of t...

The mechanism of the O(3P)+CH3CCH reaction was investigated using a combined experimental/theoretical approach. Experimentally the reaction dynamics was studied using crossed molecular beams (CMB) with mass-spectrometric detection and time-of-flight analysis at 9.2 kcal/mol collision energy. Theoretically master equation simulations were performed...

We report direct experimental/theoretical evidence that, under single collision conditions, the dominant product channels of the O(3P)+propyne and O(3P)+allene isomeric reactions lead in both cases to CO formation, but the co-products are singlet ethylidene (1CH3CH) and singlet ethylene (CH2CH2), respectively. These data, which settle a long-standi...

The combustion relevant O(3P) + C2H4 reaction stands out as a prototypical multichannel nonadiabatic reaction involving both triplet and singlet potential energy surfaces (PESs) which are strongly coupled. Crossed molecular beam (CMB) scattering experiments with universal soft electron ionization mass spectrometric detection have been used to chara...

We review the progress made in the understanding of the dynamics of the reactions of ground state oxygen atoms, O(3P), with unsaturated hydrocarbons (acetylene, ethylene, allene, propyne and propene) which are of great relevance, besides from a fundamental point of view, in combustion chemistry and of interest also in atmosphere- and astro-chemistr...

Following a recent investigation on the N(2D) + H2O reaction [Homayoon et al., J. Phys. Chem. Lett. 5, 3508 (2014)], we report on an experimental and theoretical study of the isotopologue N(2D) + D2O reaction. Crossed molecular beam (CMB) experiments were conducted at a collision energy of 10.3 kcal mol-1. Quasiclassical trajectory calculations wer...

Despite extensive kinetics/theoretical studies, information on the detailed mechanism (primary products, branching ratios (BRs)) for many important combustion reactions of O(3P) with unsaturated hydrocarbons is still lacking. We report synergic experimental/theoretical studies on the mechanism of the O(3P)+C3H6 (propene) reaction by combining cross...

Comprehension of the detailed mechanism of O(3P) + unsaturated hydrocarbon reactions is complicated by the existence of many possible channels and intersystem crossing (ISC) between triplet and singlet potential energy surfaces (PESs). We report synergic experimental/theoretical studies of the O(3P) + propene reaction by combining crossed molecular...

The N(2D) + H2O is a reaction with competitive product channels, passing through several intermediates. Dynamics of this reaction had been investigated by two of the present authors at two collision energies, Ec, using the crossed molecular beams mass spectrometric method (Faraday Discuss. 2001, 119, 27−49). The complicated mechanism of this reacti...

The O + CH3CCH reaction has been investigated in crossed molecular beam experiments at a collision energy of 38.7 kJ mol (1). Product angular and translational energy distributions have been measured for the H- and CH3-displacement channels and their relative branching ratio has been determined. The CH3-displacement channel is more important (by a...

The reaction between ground state oxygen atoms, O((3)P), and the acetylene molecule, C2H2, has been investigated in crossed molecular beam experiments with mass-spectrometric detection and time-of-flight analysis at three different collision energies, Ec = 34.4, 41.1 and 54.6 kJ mol(-1). From product angular and velocity distribution measurements o...

Experiment and theory combine to reveal quantum resonances when hydrogen molecules hit and excite oxygen molecules.

The identification of the primary products and the determination of their branching ratios as a function of translational energy for multi-channel elementary reactions of importance in combustion chemistry still represent a challenge for traditional kinetics experiments. However, this kind of information is central for the detailed modeling of comb...

Methanimine is a molecule of interest in astrobiology, as it is considered an abiotic precursor of the simplest amino acid glycine. Methanimine has been observed in the interstellar medium and in the upper atmosphere of Titan. In particular, it has been speculated that its polymerization can contribute to the formation of the haze aerosols that sur...

This paper is a detailed critical review of the production processes and reactions of N, N+, N+2, N++, and N++2 of relevance to Titan's atmosphere. The review includes neutral, ion-molecule, and recombination reactions. The review covers all possible active nitrogen species under Titan's atmospheric conditions, specifically N2 (A 3Σ+u), N (4S), N (...

The reaction involving atomic carbon in its first electronically excited state (1)D and methane has been investigated in crossed molecular beam experiments at a collision energy of 25.3 kJ mol(-1). Electronic structure calculations of the underlying potential energy surface (PES) and Rice-Ramsperger-Kassel-Marcus (RRKM) estimates of rates and branc...

The reaction of O((3)P) with C(2)H(4), of importance in combustion and atmospheric chemistry, stands out as paradigm reaction involving not only the indicated triplet state potential energy surface (PES) but also an interleaved singlet PES that is coupled to the triplet surface. This reaction poses great challenges for theory and experiment, owing...

By exploiting the potentialities of a recently implemented grid empowered molecular simulator based on the combination of collaborative interoperable service oriented computing and the usage of high performance - high throughput technologies, the results of crossed molecular beam experiments have been virtually simulated and compared with the real...

The CN + C2H4 reaction has been investigated in crossed molecular beam (CMB) experiments at a high collision energy of 42.7 kJ/mol. Differently from previous CMB experiments at lower collision energies and a room temperature multiplexed time-resolved mass spectrometry experiment, we have some indication that a second reaction channel opens, the cha...

The dynamics of the H displacement channels in the reaction N((2)D) + C(2)H(4) have been investigated by the crossed molecular beam technique with mass spectrometric detection and time-of-flight analysis at two different collision energies (17.2 and 28.2 kJ/mol). The interpretation of the scattering results is assisted by new electronic structure c...

Relating to the results presented in the paper by Professor Wester, I would to point out that, as shown for example by J. Bentley in 1980, the electronic structure of the water molecule in the gas phase is different from that is usually described in undergraduate chemistry text books. It is usually asserted that H2O is characterized by an sp3 disto...

opened the discussion of the paper by Professor Neumark by asking: I wonder if it would be possible to extend your experiments in two ways to make contact with some of the molecular beam experiments. One way is to vibra-tionally excite the anion precursor and the second is to partially deuterate it? Professor Neumark replied: With our new ion trapp...

The potential energy surface of the systems N(2D) + CH4, C2H4, and C2H6 have been investigated at B3LYP/aug-cc-pVTZ//CCSD(T)/aug-cc-pVTZ level in order to assist the interpretation of available experimental information very relevant for its implication for the chemical models of the atmosphere of Titan, and possibly of objects where both N2 and sma...

The O((3)P) + C(2)H(4) reaction, of importance in combustion and atmospheric chemistry, stands out as a paradigm reaction involving triplet- and singlet-state potential energy surfaces (PESs) interconnected by intersystem crossing (ISC). This reaction poses challenges for theory and experiments owing to the ruggedness and high dimensionality of the...

By exploiting the potentialities of a recently implemented grid empowered molecular simulator based on the combination of collaborative interoperable service oriented computing and the usage of high performance – high throughput technologies, the results of crossed molecular beam experiments have been virtually simulated and compared with the real...

We report on the determination of primary products and their branching ratios for the combustion relevant O(3P)+allene reaction by the crossed molecular beams method with soft electron-ionization mass-spectrometric detection at a collision energy of 39.3 kJ/mol. We have explored the reaction dynamics of the open channels leading to C2H4+CO, C2H2+H2...

A variety of molecular species, from simple diatoms to complex polyatomic molecules, have been identified in many gaseous extraterrestrial environments, such as the atmospheres of solar planets and satellites, exoplanets, cometary comae and the interstellar medium. The detection of relatively complex molecules can be taken as evidence that some che...

By exploiting the potentialities of collaborative work and of high throughput computing on the grid platform recently deployed within the European Grid Initiative and made available to the virtual organization COMPCHEM, it has been possible to extend GEMS, a simulator of molecular systems, to reproduce in an ab initio fashion the signal measured in...

A graphical abstract is available for this content

The reaction between sulfur atoms in the first electronically excited state, S((1)D), and methane (CH(4)), has been investigated in a complementary fashion in (a) crossed-beam dynamics experiments with mass spectrometric detection and time-of-flight (TOF) analysis at two collision energies (30.4 and 33.6 kJ mol(-1)), (b) low temperature kinetics ex...

The reaction O(1D) + HBr has been investigated by the crossed molecular beams and infrared chemiluminescence methods in an effort to characterize the dynamics of both possible reactive channels. The angular and velocity distribution of the BrO product from the O(1D) + HBr → BrO + H pathway have been obtained in crossed beam experiments at collision...

The reactions of atomic sulfur in the first excited metastable 1 D state with C 2 H 2 , C 2 H 4 , and CH 4 have been investigated at the most detailed level by means of the crossed molecular beam technique with mass spectrometric detection and ab initio calcu-lations of the relevant potential energy surfaces. The nature of the primary products and...

The dynamics of the H-displacement channels in the reaction N(2D) + C2H6 have been investigated by the crossed molecular beam technique with mass spectrometric detection and time-of-flight analysis at two different collision energies (18.0 and 31.4 kJ mol(-1)). From the derived center-of-mass product angular and translational energy distributions t...

The dynamics of the radical-radical reaction O((3)P) + CH(3), a prototypical case for the reactions of atomic oxygen with alkyl radicals of great relevance in combustion chemistry, has been investigated by means of the crossed molecular beam technique with mass spectrometric detection at a collision energy of 55.9 kJ mol(-1). The results have been...

The focus of this excellent textbook is the topic of molecular reaction dynamics. The chapters are all written by internationally recognised researchers and, from the outset, the contributors are writing with the young scientist in mind. The easy to use, stand-alone, chapters make it of value to students, teachers, and researchers alike. Subjects c...

Continuous supersonic beams of dicarbon (C2) and cyano (CN) radicals have been generated by a high-pressure radio-frequency discharge beam source starting from dilute mixtures in rare gases of suitable precursor molecules. Their internal quantum state distributions have been characterized by laser-induced-fluorescence (LIF) in a new crossed molecul...

The contribution of the first excited 11A″ state potential energy surface (PES) to the reactivity of the C(1D)+H2 system has been examined by comparing the simulations obtained with the theoretical state-to-state differential cross sections (DCSs) with experimental data from cross molecular beam experiments. The calculations were carried out using...

The reaction between sulfur atoms in the first electronically excited state, S((1)D), and ethene (C(2)H(4)) has been investigated in a complementary fashion in (a) crossed-beam dynamic experiments with mass spectrometric detection and time-of-flight (TOF) analysis at two collision energies (37.0 and 45.0 kJ mol(-1)), (b) low temperature kinetics ex...

The dynamics of the H-displacement channel in the reaction N((2)D) + CH(4) has been investigated by the crossed molecular beam (CMB) technique with mass spectrometric detection and time-of-flight (TOF) analysis at five different collision energies (from 22.2 up to 65.1 kJ/mol). The CMB results have identified two distinct isomers as primary reactio...

The reaction between excited sulfur atoms, S((1)D), and the simplest alkene molecule, ethene, has been investigated in a complementary fashion in (a) crossed-beam dynamic experiments with mass spectrometric detection and time-of-flight (TOF) analysis at a collision energy of 37.0 kJ mol(-1), (b) low temperature kinetic experiments ranging from room...

The reaction dynamics of excited sulfur atoms, S((1)D), with acetylene has been investigated by the crossed-beam scattering technique with mass spectrometric detection and time-of-flight (TOF) analysis at the collision energy of 35.6 kJ mol(-1). These studies have been made possible by the development of intense continuous supersonic beams of S((3)...

In this Perspective we highlight developments in the field of chemical reaction dynamics. Focus is on the advances recently made in the investigation of the dynamics of elementary multichannel radical-molecule and radical-radical reactions, as they have become possible using an improved crossed molecular beam scattering apparatus with universal ele...

The crossed molecular beam method with mass spectrometric detection is a versatile technique to study bimolecular reactions under single collision conditions, thus permitting us to elucidate the chemical dynamics and—in the case of polyatomic reactions—the nature of the primary products and their branching ratios. A review of the recent progress th...

The reaction between dicarbon (C2) and acetylene was recently suggested as a possible competitive reaction in the atmospheres of Titan, Saturn and Uranus by rate constant measurements at very low temperatures [see Canosa, A., Páramo, A., Le Picard, S.D., Sims, I.R., 2007. An experimental study of the reaction kinetics of C2(X1Σg+) with hydrocarbons...

This special issue of PSS is composed of selected articles based on research, presented during several different planetary meetings in 2007, including the European Geosciences Union (EGU) meeting (in particular sessions PS3.0 and PS3.1) in Vienna, Austria, from 16 to 20 April, the IUGG/IAMAS General Assembly (in particular sessions JMS12 and JMS13)...