Ab initio structural and spectroscopic study of HPSx and HSPx (x = 0,+1,−1) in the gas phase

Phosphinidenes: Fundamental Properties and Reactivity

Phosphinidenes are heavy congeners of nitrenes that have been broadly used as in situ reagents in synthetic phosphorus chemistry and also serve as versatile ligands in coordination with transition metals. However, the detection of free phosphinidenes is largely challenged by their high reactivity and also the lack of suitable synthetic methods, rendering the knowledge about the fundamental properties of this class of low-valent phosphorus compounds limited. Recently, an increasing number of free phosphinidenes bearing prototype structural and bonding properties have been prepared for the first time, thus enabling the exploration of their distinct reactivity from the nitrene analogues. This Concept article will discuss the experimental approaches for the generation of the highly unstable phosphinidenes and highlight their distinct reactivity from the nitrogen analogues so as to stimuate future studies about their potential applications in phosphorus chemistry.

State selective fragmentation of doubly ionized sulphur dioxide

Using multi-electron–ion coincidence measurements combined with high level calculations, we show that double ionisation of SO₂ at 40.81 eV can be state selective. It leads to high energy products, in good yield, via a newly identified mechanism, which is likely to apply widely to multiple ionisation by almost all impact processes.

Characterization of the simplest sulfenyl thiocyanate: isomers, spectroscopy and implications of astrophysical and biological relevance

Sulfenyl thiocyanate compounds, RSSCN, are involved in the human immune system biochemical processes. They are also the routes for the synthesis of complex S-containing species such as polypeptides, or symmetrical (RSSR) and unsymmetrical disulfides (RSSR'). At present, we have characterized the stable forms of the simplest sulfenyl thiocyanate compound, HSSCN, at the coupled cluster level. We found twenty-three isomers, for which we determined a set of structural parameters, anharmonic frequencies and reaction energies for the formation of the corresponding diatomic + triatomic and atomic + tetratomic fragments. We also discussed the implications of the present findings for biological entities containing a disulfide bridge, where we identified three isomers that may serve as prototypes. Similarities and differences with other S/N hybrid bioactive molecules are also discussed. From an astrophysical point of view, we expect HSSCN isomers to be present in astrophysical media, since several of their molecular fragments have already been detected. In sum, the present set of data can be used for the identification of HSSCN compounds and understanding the physical chemistry of sulfur containing molecules in vivo, in the laboratory and in astrophysical media.

Electronic and spectroscopic characterizations of SNP isomers

High-level ab initio electronic structure calculations were performed to characterize SNP isomers. In addition to the known linear SNP, cyc-PSN, and linear SPN isomers, we identified a fourth isomer, linear PSN, which is located ∼2.4 eV above the linear SNP isomer. The low-lying singlet and triplet electronic states of the linear SNP and SPN isomers were investigated using a multi-reference configuration interaction method and large basis set. Several bound electronic states were identified. However, their upper rovibrational levels were predicted to pre-dissociate, leading to S + PN, P + NS products, and multi-step pathways were discovered. For the ground states, a set of spectroscopic parameters were derived using standard and explicitly correlated coupled-cluster methods in conjunction with augmented correlation-consistent basis sets extrapolated to the complete basis set limit. We also considered scalar and core-valence effects. For linear isomers, the rovibrational spectra were deduced after generation of their 3D-potential energy surfaces along the stretching and bending coordinates and variational treatments of the nuclear motions.

Characterization of the electronic states of the biological relevant SSNO molecule

Using configuration interaction ab initio methods, we investigate the lowest electronic states of doublet and quartet spin multiplicities of SSNO where the one-dimensional cuts of the six-dimensional potential energy surfaces of these electronic states along the stretching and bending coordinates are computed. Mainly, these electronic states are found to be repulsive along the central SN distance. A high density of electronic states is computed even at low excitation energies that may favor their couplings. Therefore, the dynamics of the SSNO electronic states is expected to be very complex. We also characterized the bound electronic states spectroscopically where we derived their equilibrium structures and vibrational frequencies. Our calculations show the importance of taking into account of dynamical correlation, in addition to static correlation, for the accurate description of SSNO electronic excited states and more generally for those of R-NO molecular species. Finally, we highlighted the potential role of SSNO in light-induced NO delivery from SSNO related species in biological media.

Toward the laboratory identification of [O,N,S,S] isomers: Implications for biological NO chemistry

Benchmark ab initio calculations are performed to investigate the stable isomers of [O,N,S,S]. These computations are carried out using coupled cluster (RCCSD(T)) and explicitly correlated coupled cluster methods (RCCSD(T)-F12). In addition to the already known cis isomer of SSNO, nine other stable forms are predicted. The most stable isomer is cis-OSNS. Nine structures are chain bent-bent with relatively large dipole moments which make them detectable, as cis-SSNO, by infrared, far-infrared, and microwave spectroscopies. We found also a C2v isomer (NS2O). Since these species are strongly suggested to play an important role as intermediates during the bioactive reaction products of the NO/H2S interaction, the rotational and vibrational spectroscopic parameters are presented to help aid the in vivo identification and assignment of these spectra. Results from this work show that [O,N,S,S] may play key roles during nitric oxide transport and deliver in biological media, as well as, provide an explanation for the weak characteristic of disulfide bridges within proteins.

Tailoring the electronic properties among oxoarsine, arsinoyl and arsine oxide isomers: the simplest molecular systems with an arsenic–oxygen bond

The main goal of this investigation is to understand the reaction pathways and the electronic and spectroscopy properties of AsOH_n radicals (n = 0–3), which are some of the simplest compound models with an arsenic–oxygen bond.

Theoretical spectroscopic investigations of HNS(q) and HSN(q) (q = 0, +1, -1) in the gas phase

We performed accurate ab initio investigations of the geometric parameters and the vibrational structure of neutral HNS/HSN triatomics and their singly charged anions and cations. We used standard and explicitly correlated coupled cluster approaches in connection with large basis sets. At the highest levels of description, we show that results nicely approach those obtained at the complete basis set limit. Moreover, we generated the three-dimensional potential energy surfaces (3D PESs) for these molecular entities at the coupled cluster level with singles and doubles and a perturbative treatment of triple excitations, along with a basis set of augmented quintuple-zeta quality (aug-cc-pV5Z). A full set of spectroscopic constants are deduced from these potentials by applying perturbation theory. In addition, these 3D PESs are incorporated into variational treatment of the nuclear motions. The pattern of the lowest vibrational levels and corresponding wavefunctions, up to around 4000 cm(-1) above the corresponding potential energy minimum, is presented for the first time.