Gold with +4 oxidation state compounds: mass spectrometric and theoretical characterization of AuO2.

Using an ab initio methodology and mass spectrometric study we identify AuO2+ as a metastable species in the gas phase. This represents the first characterization of a gas phase compound of gold with the oxidation state +4. Computations show that this dication exhibits deep potential wells with long lived electronic states. Its electronic ground state is of 4∑- symmetry, which is known for very few molecular ground states. We also discussed the O + Au2+ collision dynamics, which leads mostly to charge transfer to form Au+ and O+ species. This identification may help in identifying new routes for the reactivity of gold in the gas phase, in solution and in the condensed phase.

Spectroscopy and characterization of AlNX (X = O and S): Triatomic circumstellar molecules.

Three isomers of the triatomic [Al, N, O] molecular system have been observed in a solid argon matrix by infrared absorption spectroscopy using 15N and 18O isotopic substitution. The present work provides high-level quantum chemical predictions of their spectroscopic parameters to observe this system in the interstellar medium. The spectroscopic parameters, stability, and geometries of the lowest stable isomers of its isoelectronic system [Al, N, S] were characterized using coupled-cluster CCSD(T), explicitly correlated coupled-cluster CCSD(T)-F12, and multireference configuration interaction. The three-dimensional potential energy surfaces of all isomers were computed at the CCSD(T)-F12/aug-cc-pV5Z level, and a set of spectroscopic parameters were calculated. In both systems, the most stable isomer is linear with an X3Σ- electronic ground state, and all linear isomers are characterized by small bending modes of less than 200 cm-1. Due to their large dipole moments, the high intensities of such modes, and the nonexistence of anharmonic resonance complicating their spectra, our results facilitate the detection of AlNO and AlNS in the laboratory or in the interstellar medium.

Copper-Chalcogen Bonds in Olfaction: Accurate ab Initio Characterization of CuSH and CuOH.

From highly correlated ab initio methods at the CCSD(T) level, with and without the inclusion of scalar relativistic effects, accurate 3D potential energy surfaces (PESs) of CuSH and CuOH were generated in their electronic ground state. The PESs are incorporated into perturbative and variational treatments of nuclear motions. Using these approaches, we derived a set of accurate spectroscopic parameters and the pattern of the vibrational states of CuXH (X = O,S) up to 4000 cm-1. The applied calculations at the CCSD(T)/aug-cc-pV5Z-DK level of theory are validated using several experimental high-resolution spectroscopy data (including rotational spectroscopy) available in the literature. The optimized equilibrium geometries of CuSH and CuOH with bending angles of 93.9° and 110.2°, Cu-X bond lengths of 2.088 and 1.764 Å, and X-H bond lengths of 1.344 and 0.961 Å, respectively, accurately reproduce the experimental structures and clearly show the importance of the scalar relativistic effects. The anharmonic frequencies, ν1, ν2, and ν3, are computed at 3655.5, 746.3, and 623.3 cm-1 for CuOH and at 2572.9, 588.9, and 396.6 cm-1 for CuSH, respectively. Finally, the PESs are derived as anharmonic force fields for CuXH (X = O, S) that can be incorporated into large scale molecular dynamics simulations of Cu-X containing compounds. The results are discussed within the scope of available literature on the effects of substitution of oxygen by sulfur for putative molecular recognition mechanisms.

Spectroscopy and Stability of AlOP: A Possible Progenitor of Interstellar Metal.

Standard and explicitly correlated coupled-cluster theory computations in conjunction with large basis sets are performed to characterize [Al,P,O] isomers. Three isomers, namely, linear-AlOP, bent-AlOP, and linear-OAlP, are found to be stable species. Their optimized equilibrium geometries, harmonic vibrational frequencies, rotational constants, and relative energies are deduced. In addition, a set of spectroscopic parameters is generated from the three-dimensional potential energy surfaces of each isomer at the (R)CCSD(T)/aug-cc-pV5Z level. The linear isomers have an X3Σ- electronic ground state and are characterized as weakly bound systems or floppy molecules due to their low-frequency bending modes (<150 cm-1). The dipole moment of linear-AlOP is calculated to be 1.48 D. By comparison, a much larger dipole moment is computed for linear-OAlP (5.01 D), indicating lower ionic character in AlOP. Both the linear-OAlP and linear-AlOP isomers are suggested to be good candidates for detection in interstellar media by radio astronomy.

Spectroscopy of the electronic excited states of thioxophosphane, HPS, and of its deuterated species.

The stable low energy states of the HPS and DPS molecules have been studied through multi-reference ab initio methods in conjunction with large atomic basis sets. Stable states for these species have been examined up to 7 eV above the ground state minimum. We found six stable electronic states that are mostly mono-configurational. These states may be involved in the photodynamics and photodissociation of this molecule. In particular, the 2 1A' state presents two minima on the potential energy surface, one of them close to linear configuration. This state may be populated after the absorption of a visible photon from the ground state and gives rise to large amplitude motions that may eventually induce isomerization to electronically excited HSP. Moreover, we characterized these states spectroscopically to facilitate the assignment of the vibronic spectra of the HPS and DPS species. For these low-energy states, we thus computed vertical and adiabatic excitation energies, and for the stable ones, a full set of spectroscopic constants including harmonic frequencies and anharmonic vibrational, rotational, and centrifugal distortion constants. The calculated potential energy surfaces for these states have been used in a variational procedure to deduce the pattern of vibrational levels up to 4000 cm-1 above the corresponding vibrationless level. Our data may serve for the assignment of the IR and Vis spectra of HPS and DPS.

Disentangling the complex spectrum of the ethynyl cation.

The ethynyl cation, C2H+, is of great importance in astrophysical media and in combustion. It is involved in the formation of larger organic compounds and in their decomposition mechanisms. Here, we investigate the low-lying electronic states of this cation using pure ab initio methodologies. The evolution of its potential energy surfaces along the stretching and bending coordinates reveals a high density of electronic states that favours mutual interactions and the mixing of wavefunctions. The ground state is of 3Π space symmetry and the lowest singlet state (1Π) is found to be a quasi-linear-quasi-linear Renner-Teller system. Our work suggests that the (spin-)rovibronic spectrum of such a molecular system is complicated, because of the contributions of multiple couplings, including Renner-Teller, vibronic and spin-orbit. We also deduced the adiabatic ionization energy of the ethynyl radical, in good agreement with recent measurements. In summary, our work shows that the ethynyl cation, in spite of its small size, still represents a challenging molecular problem to be solved.

The use of pain drawings in screening for psychological involvement in complaints of low-back pain.

The pain drawings of 54 low-back-pain patients were examined to find out if it is possible to use them as a brief screening test in order to assess the psychological impairment of the patients. We were using the scoring system of Ransford et al, which we slightly changed, and chose as a criterion variable the ERMSS (Erweiterte Revidierte Mehrdimensionale Schmerzskala) of Cziske. This test originates in the McGill Pain Questionnaire of Melzack and Torgerson; its scales describe four dimensions of pain perception: pain intensity, the sensory-discriminative dimension reflecting the somatic aspect of pain; the affective-motivational dimension, and the total number of words, both representing the psychological involvement of a pain patient. A correlation was found between pain drawing score and the sensory-discriminative dimension of pain perception, whereas there was no such correlation between drawing score and the affective dimension. These results indicate that the pain drawing score might not be a sufficiently valid instrument for assessing psychological disturbances in pain patients to allow it to be used for individual diagnosis without hesitation.