Is AlOH the Astrochemical Reservoir Molecule of AlO?: Insights from Excited Electronic States

Very recently, the optical bands of the 2Σ+ ← X2Σ+system of AlO have been identified in the red supergiant star VYCMa. In an effort to explain the origin of this transition, we used state-of-the-art quantum chemical calculations with proven high accuracy to compute the lowest singlet and triplet electronic states of the AlOH and HAlO isomers as well as their equilibrium geometry and electronic properties. Our calculated potential energy surfaces implicate the three singlet electronic states 21A′, 31A′, and 11A″ in the photodissociation of the [Al,O,H] system. Only AlO, H, Al, and OH products can occur through the photodissociation of [Al,O,H]; AlH and O are not allowed. For the photodissociation of AlOH, the AlO product can occur only in its excited states AlO(2Π) and AlO(2Σ+)

An Ab Initio Study of the Structures, Vibrational Spectra, and Energetics of AlSHX (X = –1, 0, +1)

The ground state of aluminum hydrosulfide, AlSHX (where X = − 1,0, + 1), has been examined using high-level ab initio electronic structure calculations at the CCSD(T) level with an augmented correlation-consistent basis set. The geometries have been optimized up through the aug-cc-pV5Z level and vibrational frequencies calculated using the aug-cc-pV5Z basis set. The energetic properties of AlSH are also examined. The adiabatic ionization potential and electron affinity of AlSH are calculated to be 198.5 and 7.7 kcal mol−1, respectively. Dissociation of AlSH into AlS + H will require 78.2 kcal mol−1 of energy, and the Al-S bond energy is 91.1 kcal mol−1. Structural and energetic properties of the cation and anion of AlSH are reported for the first time

Role of OH-stretch/torsion coupling and quantum yield effects in the first OH overtone spectrum of cis-cis HOONO

A joint theoretical and experimental investigation is undertaken to study the effects of OH-stretch/HOON torsion coupling and of quantum yield on the previously reported first overtone action spectrum of cis-cis HOONO (peroxynitrous acid). The minimum energy path along the HOON dihedral angle is computed at the coupled cluster singles and doubles with perturbative triples level with correlation consistent polarized quadruple zeta basis set, at the structure optimized using the triple zeta basis set (CCSD(T)/cc-pVQZ//CCSD(T)/cc-pVTZ). The two-dimensional ab initio potential energy and dipole moment surfaces for cis-cis HOONO are calculated as functions of the HOON torsion and OH bond length about the minimum energy path at the CCSD(T)/cc-pVTZ and QCISD/AUG-cc-pVTZ (QCISD—quadratic configuration interaction with single and double excitation and AUG-augmented with diffuse functions) level of theory/basis, respectively. The OH-stretch vibration depends strongly on the torsional angle, and the torsional potential possesses a broad shelf at ~90°, the cis-perp conformation. The calculated electronic energies and dipoles are fit to simple functional forms and absorption spectra in the region of the OH fundamental and first overtone are calculated from these surfaces. While the experimental and calculated spectra of the OH fundamental band are in good agreement, significant differences in the intensity patterns are observed between the calculated absorption spectrum and the measured action spectrum in the 2nuOH region. These differences are attributed to the fact that several of the experimentally accessible states do not have sufficient energy to dissociate to OH+NO2 and therefore are not detectable in an action spectrum. Scaling of the intensities of transitions to these states, assuming D0=82.0 kJ/mol, is shown to produce a spectrum that is in good agreement with the measured action spectrum. Based on this agreement, we assign two of the features in the spectrum to Delta n=0 transitions (where n is the HOON torsion quantum number) that are blue shifted relative to the origin band, while the large peak near 7000 cm^–1 is assigned to a series of Delta n=+1 transitions, with predominant contributions from torsionally excited states with substantial cis-perp character. The direct absorption spectrum of cis-cis HOONO (6300–6850 cm^–1) is recorded by cavity ringdown spectroscopy in a discharge flow cell. A single band of HOONO is observed at 6370 cm^–1 and is assigned as the origin of the first OH overtone of cis-cis HOONO. These results imply that the origin band is suppressed by over an order of magnitude in the action spectrum, due to a reduced quantum yield. The striking differences between absorption and action spectra are correctly predicted by the calculations

Toward the detection of the triatomic negative ion SPN−: Spectroscopy and potential energy surfaces

High level theoretical calculations using coupled-cluster theory were performed to provide an accurate description of the electronic structure, spectroscopic properties, and stability of the triatomic negative ion comprising S, N, and P. The adiabatic electron affinities (AEAs) and vertical detachment energies (VDEs) of PNS, SPN, PSN, and cyc-PSN were calculated. The predicted AEA and VDE of the linear SPN isomer are large: 2.24 and 3.04 eV, respectively. The potential energy surfaces (PESs) of the lowest-lying electronic states of the SPN isomer along the PN and SP bond lengths and bond angle were mapped. A set of spectroscopic parameters for SPN, PNS, and PSN in their electronic ground states is obtained from the 3D PESs to help detect these species in the gas phase. The electronic excited state SPN (12A”) is predicted to be stable with a long lifetime calculated to be 189.7 µs. The formation of SPN in its electronic ground state through the bimolecular collision between S + PN and N + PS is also discussed

Cis-cis and trans-perp HOONO: Action spectroscopy and isomerization kinetics

The weakly bound HOONO product of the OH + NO_2 + M reaction is studied using the vibrational predissociation that follows excitation of the first OH overtone (2nu1). We observe formation of both cis-cis and trans-perp conformers of HOONO. The trans-perp HOONO 2nu1 band is observed under thermal (223–238 K) conditions at 6971 cm^(–1). We assign the previously published (warmer temperature) HOONO spectrum to the 2nu1 band at 6365 cm^(–1) and 2nu1-containing combination bands of the cis-cis conformer of HOONO. The band shape of the trans-perp HOONO spectrum is in excellent agreement with the predicted rotational contour based on previous experimental and theoretical results, but the apparent origin of the cis-cis HOONO spectrum at 6365 cm^(–1) is featureless and significantly broader, suggesting more rapid intramolecular vibrational redistribution or predissociation in the latter isomer. The thermally less stable trans-perp HOONO isomerizes rapidly to cis-cis HOONO with an experimentally determined lifetime of 39 ms at 233 K at 13 hPa (in a buffer gas of predominantly Ar). The temperature dependence of the trans-perp HOONO lifetime in the range 223–238 K yields an isomerization barrier of 33±12 kJ/mol. New ab initio calculations of the structure and vibrational mode frequencies of the transition state perp-perp HOONO are performed using the coupled cluster singles and doubles with perturbative triples [CCSD(T)] model, using a correlation consistent polarized triple zeta basis set (cc-pVTZ). The energetics of cis-cis, trans-perp, and perp-perp HOONO are also calculated at this level [CCSD(T)/cc-pVTZ] and with a quadruple zeta basis set using the structure determined at the triple zeta basis set [CCSD(T)/cc-pVQZ//CCSD(T)/cc-pVTZ]. These calculations predict that the anti form of perp-perp HOONO has an energy of DeltaE0 = 42.4 kJ/mol above trans-perp HOONO, corresponding to an activation enthalpy of DeltaH298[double-dagger]0 = 41.1 kJ/mol. These results are in good agreement with statistical simulations based on a model developed by Golden, Barker, and Lohr. The simulated isomerization rates match the observed decay rates when modeled with a trans-perp to cis-cis HOONO isomerization barrier of 40.8 kJ/mol and a strong collision model. The quantum yield of cis-cis HOONO dissociation to OH and NO2 is also calculated as a function of photon excitation energy in the range 3500–7500 cm^(–1), assuming D0 = 83 kJ/mol. The quantum yield is predicted to vary from 0.15 to 1 over the observed spectrum at 298 K, leading to band intensities in the action spectrum that are highly temperature dependent; however, the observed relative band strengths in the cis-cis HOONO spectrum do not change substantially with temperature over the range 193–273 K. Semiempirical calculations of the oscillator strengths for 2nu1(cis-cis HOONO) and 2nu1(trans-perp HOONO) are performed using (1) a one-dimensional anharmonic model and (2) a Morse oscillator model for the OH stretch, and ab initio dipole moment functions calculated using Becke, Lee, Yang, and Parr density functional theory (B3LYP), Møller-Plesset pertubation theory truncated at the second and third order (MP2 and MP3), and quadratic configuration interaction theory using single and double excitations (QCISD). The QCISD level calculated ratio of 2nu1 oscillator strengths of trans-perp to cis-cis HOONO is 3.7:1. The observed intensities indicate that the concentration of trans-perp HOONO early in the OH + NO2 reaction is significantly greater than predicted by a Boltzmann distribution, consistent with statistical predictions of high initial yields of trans-perp HOONO from the OH + NO_2 + M reaction. In the atmosphere, trans-perp HOONO will isomerize nearly instantaneously to cis-cis HOONO. Loss of HOONO via photodissociation in the near-IR limits the lifetime of cis-cis HOONO during daylight to less than 45 h, other loss mechanisms will reduce the lifetime further

The thermal and electrical properties of the promising semiconductor MXene Hf2CO2

In this work, we investigate the thermal and electrical properties of oxygen-functionalized M2CO2 (M = Ti, Zr, Hf) MXenes using first-principles calculations. Hf2CO2 is found to exhibit a thermal conductivity better than MoS2 and phosphorene. The room temperature thermal conductivity along the armchair direction is determined to be 86.25-131.2 Wm-1K-1 with a flake length of 5-100 um, and the corresponding value in the zigzag direction is approximately 42% of that in the armchair direction. Other important thermal properties of M2CO2 are also considered, including their specific heat and thermal expansion coefficients. The theoretical room temperature thermal expansion coefficient of Hf2CO2 is 6.094x10-6 K-1, which is lower than that of most metals. Moreover, Hf2CO2 is determined to be a semiconductor with a band gap of 1.657 eV and to have high and anisotropic carrier mobility. At room temperature, the Hf2CO2 hole mobility in the armchair direction (in the zigzag direction) is determined to be as high as 13.5x103 cm2V-1s-1 (17.6x103 cm2V-1s-1), which is comparable to that of phosphorene. Broader utilization of Hf2CO2 as a material for nanoelectronics is likely because of its moderate band gap, satisfactory thermal conductivity, low thermal expansion coefficient, and excellent carrier mobility. The corresponding thermal and electrical properties of Ti2CO2 and Zr2CO2 are also provided here for comparison. Notably, Ti2CO2 presents relatively low thermal conductivity and much higher carrier mobility than Hf2CO2, which is an indication that Ti2CO2 may be used as an efficient thermoelectric material.Comment: 26 pages, 5 figures, 2 table

Differences in Electronic Structure of Global Warming Molecules Lead to Different Molecular Properties. Reply to Wallington et al.

No abstract availabl

Hydrogen bonding in cubic (H_2O)_8 and OH∙(H_2O)_7 clusters

A systematic study is presented for OH∙(H_2O)_7 clusters derived from the cubic (H_2O)_8 octamer by replacing one water with a hydroxyl radical. The system is a prototype for atmospheric water clusters containing the environmentally important OH species, and for OH adsorbed at the surface of ice. The full set of 39 symmetry-distinct cubic OH∙(H_2O)_7 clusters is enumerated, and the structures are determined using ab initio quantum chemical methods. Graph invariants are employed to obtain a unified analysis of the stability and structure of cubic (H_2O)_8 and OH∙(H_2O)_7, relating these physical properties to the various hydrogen-bond topologies present in these clusters. To accomplish this the graph invariant formalism is extended to treat a hydrogen bonding impurity within a pure water network

SPECTROSCOPY OF JUPITER'S ATMOSPHERE: INSIGHTS FROM DFT AND AB-INITIO CALCULATIONS

Despite several space mission and astronomical observation made from earth, the structure, color and mode of formation of Jupiter planet and other Jovian planet remain largely unknown. Understanding the atmosphere, haze and the colors of these planets, especially the great red spot (GRS) of Jupiter and its belts are still a big challenge for both experimenters and theorists. Jupiter’s colors range from blue to orange with some green regions. The most important chemical components that are responsible for the coloring of Jupiter and other Jovian planets are mainly CH4, NH4SH, H2O and NH3 [1-3]. Although an explanation for the color of Jupiter have been suggested to involve these species or other related molecules arise from the interaction between these species in gas phase. In this report, we present our studies on the color of Jupiter. We have examined the electronic structure, stability infra-red and UV-Vis spectroscopy of NH4SH and other related molecules in crystalline and gas phase using Density Functional Theory (DFT) and ab-initio methods, are we report new insights from the spectroscopy NH4SH in explaining the different color regions of Jupiter. References: 1.Roman, M.T., Banfield, D., Gierasch, P.J., Icarus, 225, 93 (2013). 2.Atreya,S.K et al., Planet Space Sci., 47, 1243 (1999). 3.Weidenschilling, S.J., Lewis, J.S., Icarus 20, 465 (1973)