Rotational excitation of the interstellar HCO+ by para-H2(j = 0) is investigated. The scattering calculations are based on a new potential energy surface (PES) for HCO+–H2 van der Waals complex averaged over H2 orientations and considering both molecules as rigid rotors. ab initio PES was obtained from electronic structure using single double coupled cluster method with perturbative contributions connected triple excitations [CCSD(T)]. five atoms were described augmented...

Abstract Given its abundance in the interstellar medium recently justified by astronomical observations, chemistry and reactivity of metal-bearing molecule MgS require special attention. The availability up-to-date collision data between this most abundant perturbing species H2 He is an essential resource to derive reliable values molecular from observations. This work aims provide improved scattering parameters for system with He. A new two-dimensional potential energy surface (2D-PES)...

Bromine atom (Br) reactions lead to ozone depletion in the troposphere and stratosphere. Photodegradation of bromocarbons is one main sources bromine atoms atmosphere. Here, we use high-level ab initio methods, including spin-orbit effects, study photodissociation CH2Br radical. All possible fragmentation pathways, namely + hν → CH2 Br, HCBr H, CBr H2, have been analyzed. Potential-energy curves ground several excited electronic states along corresponding dissociating bond distance each...

We used multiconfigurational methods and a large basis set to compute the potential energy curves of valence valence-Rydberg electronic states MgO molecule. New bound are found. Using these highly correlated wave functions, we evaluated their mutual spin-orbit couplings transition moment integrals. For MgO, deduced an accurate spectroscopic constants that agree remarkably well with experimental results. Moreover, our potentials, moments, coupling evolutions incorporated into Fermi golden...

Highly correlated ab initio methods are used to investigate the lowest electronic states of doublet and quartet spin multiplicities for SNO. One-dimensional cuts three-dimensional potential energy surfaces (3D-PESs) these along stretch bend coordinate calculated. Several avoided crossings conical intersections located bent linear configurations. The dynamics on excited SNO very complex, suggest that multi-step mechanisms should occur populate ground state via radiationless processes or lead...

Three-dimensional potential energy surfaces (PESs) have been calculated for the lowest electronic states of NCO, CNO and CON isomers, using internally contracted Multi Reference Configuration Interaction (MRCI) Coupled-Clusters RCCSD(T) ab initio methods. For low lying doublet quartet excited three N–CO, O–CN, C–NO C–ON collinear dissociation paths were mapped by Complete Active Space SCF (CASSCF) approach variations with bending coordinate explored. Several regions conical intersections...

The low-energy electronic states of NSO anion and its SNO isomeric form for the singlet, triplet, quintet spin multiplicities have been investigated by accurate ab initio approaches large atomic basis sets. One-dimensional cuts three-dimensional potential energy surfaces (PESs) along selected interatomic distances bending angles these calculated to assess formation stability NSO− SNO− in gas phase. Results show that anions two (X̃1A′ 13A″) are bound stable with respect electron detachment....

Small methane clusters (CH4)n are irradiated using intense femtosecond laser excitation at 624 nm. The ionized species and those resulting from their fragmentation detected via time-of-flight mass spectrometry (TOF MS). We find evidence of bound, multiply charged molecules Coulomb explosion upon exposure to highly energetic, ultrafast radiation. assignment the spectra is done after first-principles calculations (at (R)MP2/aug-cc-pVXZ (X = D,T) level) on (CH4)nq+ (n 1–4, q 1–4). also...

We used ab initio methodology for the computation of potential energy curves doublet and quartet electronic states MgO+ cation correlating with four lowest dissociation limits. Using these highly correlated wavefunctions, we calculated their spin–orbit coupling transition moments. deduced an accurate set spectroscopic constants this cation. Most data relative to excited are predictive in nature. Moreover, our potentials, moments evolutions incorporated into Fermi golden rule calculations...

The weakly bound charge transfer OMgOO+(2Π) ion is a quasi-linear–bent Renner–Teller system with non-zero spin–orbit contribution. six-dimensional potential energy surfaces (6D-PESs) for the two components have been generated in internal coordinates. After benchmarking calculations, we show that newly implemented explicitly correlated coupled cluster approach (RCCSD(T)-F12) connection cc-pVTZ-F12 basis set provides an accurate description of full 6D-PESs this molecular system. Both are bent...

Full-dimensional semiclassical dynamical calculations combining classical paths and Bohr quantization of product internal motions are reported for the prototype photofragmentation isocyanic acid in S1 state. These allow one to closely reproduce first time key features state-of-the-art imaging measurements at photolysis wavelengths 201 210 nm while providing insight into underlying dissociation mechanism. Quantum scattering being beyond reach most polyatomic fissions, pair-correlated data on...

Using ab initio methodology, we studied the IOq+ (q = 2, 3, 4) multi-charged ions. Benchmark computations on IO(X2Π) neutral species allow validate current procedure. For IO2+, several potential wells were found ground and electronic excited states potentials with barriers respect to dissociation, where this dication can exist in gas phase as long-lived metastable molecules. We confirm hence recent observation of by mass spectrometry. Moreover, predict existence IO3+ trication, a shallow...

Peroxyacetic acid, a non-rigid oxygenated organic molecule which acts in the atmosphere as reservoir of HO X and RO radicals, is studied using highly correlated ab initio methods with aim its spectroscopic characterization gas phase.

Photodissociation of the CH2Cl radical is investigated by using high-level multireference configuration interaction ab initio methods, including spin–orbit coupling. All possible fragmentation pathways, namely, + hν → CH2 Cl, HCCl H, and CCl H2, have been analyzed. The potential-energy curves ground several excited electronic states along corresponding dissociating bond distance each pathway calculated. Inclusion couplings found to be crucial because it strongly determines shape different...

Potential-energy surfaces and spin–orbit couplings involved in the photodissociation of CH₃O CH₃S radicals have been investigated.

Spectroscopic and structural properties of methoxymethyl radical (CH$_3$OCH$_2$, RDME) are determined using explicitly correlated ab initio methods. This astrophysical atmospheric relevance has not been fully characterized at low temperatures, which delayed the searches. We provide rovibrational parameters, excitations to energy electronic states, torsional inversion barriers vibrational levels. In ground state (X$^2$A), appears "clean" from non-adiabatic effects, minimum structure is an...

Two ketones of atmospheric interest, methyl glyoxal and vinyl ketone, are studied using explicitly correlated coupled cluster theory core–valence correlation-consistent basis sets. The work focuses on the far-infrared region. At employed level theory, rotational constants can be determined to within a few megahertz experimental data. Both molecules present two conformers, trans/cis antiperiplanar (Ap)/synperiplanar (Sp), respectively. trans-Methyl Ap-methyl ketone preferred structures....

Ab initio studies on CHx(OH)4−x (x = 0-3) polyols are carried out to derive their structural and spectroscopic features. Several stereoisomers (both equilibrium structures transition states) found. Some predicted here for the first time. We determined hence geometrical parameters, vibrational frequencies, electronic excitation energies singlet manifold, IR spectra. While spectra all present similar shapes, UV exhibit however distinct band origin that specific each polyol more interestingly...

The discovery of anions in the interstellar medium has shown that they are very reactive species.

The C–C bond dissociation channel of the ethyl (CH3–CH2) radical is investigated at 197.4, 199.98 and 201 nm by velocity map imaging resonance enhanced multiphoton ionisation (REMPI) detection produced CH3 fragments. On light high-level ab initio calculations performed in this work, up to four pathways are identified leading, respectively, ground state radicals correlation with CH2 fragments first electronic states. major pathway associated threshold over an exit barrier located point a...

Accurate ab initio calculations are performed to investigate the stable isomers of [MgO3]+ and its lowest electronic states at both molecular asymptotic regions. The done using large basis sets configuration interaction methods including complete active space self-consistent field, internally contracted multi-reference interaction, standard coupled cluster (RCCSD(T)) approaches newly implemented explicitly correlated method (RCCSD(T)-F12). presence three forms is predicted: a cyclic global...

Methoxymethanol (CH3OCH2OH), an oxygenated volatile organic compound of low stability detected in the interstellar medium, represents example nonrigid molecules showing various interacting and inseparable large-amplitude motions. The species discloses a relevant coupling among torsional modes, strong enough to prevent complete assignments using effective Hamiltonians reduced dimensionality. Theoretical models for rotational spectroscopy can improve if they treat three vibrational coordinates...