1A1 Electronic State Research Articles

BeM(CO)3- (M = Co, Rh, Ir) and BeM(CO)3 (M = Ni, Pd, Pt): Triply bonded terminal beryllium in zero oxidation state.

We perform detailed potential energy surface explorations of BeM(CO)3- (M = Co, Rh, Ir) and BeM(CO)3 (M = Ni, Pd, Pt) using both single-reference and multireference-based methods. The present results at the CASPT2(12,12)/def2-QZVPD//M06-D3/def2-TZVPPD level reveal that the global minimum of BeM(CO)3- (M = Co, Rh, Ir) and BePt(CO)3 is a C3v symmetric structure with an 1A1 electronic state, where Be is located in a terminal position bonded to M along the center axis. For other cases, the C3v symmetric structure is a low-lying local minimum. Although the present complexes are isoelectronic with the recently reported BFe(CO)3- complex having a B-Fe quadruple bond, radial orbital-energy slope (ROS) analysis reveals that the highest occupied molecular orbital (HOMO) in the title complexes is slightly antibonding in nature, which bars a quadruple bonding assignment. Similar weak antibonding nature of HOMO in the previously reported BeM(CO)4 (M = Ru, Os) complexes is also noted in ROS analysis. The bonding analysis through energy decomposition analysis in combination with the natural orbital for chemical valence shows that the bonding between Be and M(CO)3q (q = -1 for M = Co, Rh, Ir and q = 0 for M = Ni, Pd, Pt) can be best described as Be in the ground state (1S) interacting with M(CO)30/- via dative bonds. The Be(spσ) → M(CO)3q σ-donation and the complementary Be(spσ) ← M(CO)3q σ-back donation make the overall σ bond, which is accompanied by two weak Be(pπ) ← M(CO)3q π-bonds. These complexes represent triply bonded terminal beryllium in an unusual zero oxidation state.

Geometrical and electronic structure of the molybdenum and tungsten halides MX3 and MX4 (M = Mo, W; X = F, Cl): Jahn-Teller effect and spin-orbit coupling

The ground and lower-lying excited electronic states of MX3 and MX4 (M = Mo, W; X = F, Cl) molecules were systematically studied by the complete active space self-consistent field (CASSCF) and multiconfigurational quasi-degenerate second-order perturbation (XMCQDPT2) methods. Scalar-relativistic effects and spin-orbit coupling were taken into account employing the third-order Douglas-Kroll-Hess (DKH) Hamiltonian and full Breit-Pauli operator. The ground orbital state of MoF3 and MoCl3 complexes is quadruplet 4A2′ state in the equilibrium configuration with D3h symmetry. If the spin-orbit interaction is taken into account the calculations result in two 4E1/2 and 4E3/2 spin-orbit states with 11–14 cm−1 energy differences instead of one 4A2′ state. Spin-orbit interaction quenches the Jahn-Teller effect in 2E″ ground orbital state of WF3 complex in D3h configuration, and C2v configuration with (4E1/2 + 4E3/2) spin-mixed state corresponds to the minimum on the PES. The WCl3 complex reveals strong interaction of the spin-orbit states of different multiplicity. For WCl3 complex the configuration with D3h symmetry corresponds to the minimum on the PES for four lowest spin-mixed electronic states. The MoF4, MoCl4 and WCl4 complexes possess the tetrahedral equilibrium configuration with 3A2 orbital electronic state. If the spin-orbit interaction is taken into account the ground state changes to the threefold degenerated 3T2 spin-orbit state with weak Jahn-Teller effect. In the case of WF4 complex the strong Jahn-Teller effect has been discovered in the first excited 1E singlet electronic state of the tetrahedral structure, and D2d configuration with 1A1 electronic state possesses the lowest energy. The comparison with available experimental data has been performed. The tendencies in molecular parameters of complexes studied were analyzed.

On the Highest Oxidation States of Metal Elements in MO4 Molecules (M = Fe, Ru, Os, Hs, Sm, and Pu)

Metal tetraoxygen molecules (MO4, M = Fe, Ru, Os, Hs, Sm, Pu) of all metal atoms M with eight valence electrons are theoretically studied using density functional and correlated wave function approaches. The heavier d-block elements Ru, Os, Hs are confirmed to form stable tetraoxides of Td symmetry in (1)A1 electronic states with empty metal d(0) valence shell and closed-shell O(2-) ligands, while the 3d-, 4f-, and 5f-elements Fe, Sm, and Pu prefer partial occupation of their valence shells and peroxide or superoxide ligands at lower symmetry structures with various spin couplings. The different geometric and electronic structures and chemical bonding types of the six iso-stoichiometric species are explained in terms of atomic orbital energies and orbital radii. The variations found here contribute to our general understanding of the periodic trends of oxidation states across the periodic table.

Measurement and Control of Single Nitrogen-Vacancy Center Spins above 600 K

We study the spin and orbital dynamics of single nitrogen-vacancy (NV) centers in diamond between room temperature and 700 K. We find that the ability to optically address and coherently control single spins above room temperature is limited by nonradiative processes that quench the NV center's fluorescence-based spin readout between 550 and 700 K. Combined with electronic structure calculations, our measurements indicate that the energy difference between the 3E and 1A1 electronic states is approximately 0.8 eV. We also demonstrate that the inhomogeneous spin lifetime (T2*) is temperature independent up to at least 625 K, suggesting that single NV centers could be applied as nanoscale thermometers over a broad temperature range.

Wavefunction overlap effects in the collisional excitation of NH3 by slow molecular ions

Collisional excitation of ammonia from the ground 1A1 electronic state to various optically-allowed and dipole-forbidden states has been studied in 1.8 keV collisions with H2+, N2+, O2+ and CO2+ projectiles by energy loss spectrometry using a high-resolution ion translational energy spectrometer. The collisional excitation cross section is found to be sensitively dependent on whether the projectile ion is of Sigma or Pi symmetry. This dependence is interpreted as a manifestation of wavefunction overlap effects involving the highest occupied molecular orbitals of the target and projectile ions. Results of concomitant theoretical calculations of overlap integrals for different orientations of each projectile-target system provide support for the wavefunction overlap picture.

A multireference configuration interaction study of the low-lying electronic states of ClO+2 and the X 1A1 state of ClO−2

Near-equilibrium two-dimensional (C2v symmetry) potential energy functions of the first seven electronic states of ClO2+ and the ground X 1A1 electronic state of ClO2− have been calculated using internally contracted multireference configuration interaction (CMRCI) wave functions. In the case of ClO2+, five electronic states (3B2, 3A2, 1A2, 3B1, and 1B1) are predicted to lie within 3 eV of the X 1A1 ground state, while a 1B2 state has a calculated Te of just over 5 eV. In the X state, the equilibrium geometry is calculated by CMRCI to be re=1.423 Å and θe=120.8°. Harmonic vibrational frequencies of 1012 (ω1), 511 (ω2), and 1283 cm−1 (ω3) were derived from the computed potential energy function, and ω1 and ω2 were found to be in good agreement with the values estimated from the photoelectron spectrum of ClO2. For the X 1A1 state of ClO2−, calculated spectroscopic constants include re=1.573 Å, θe=113.9°, ω1=789 cm−1, ω2=378 cm−1, and ω3=848 cm−1. Electric dipole moment functions have also been derived for both species in their electronic ground states. The calculated equilibrium dipole moments for ClO2+ and ClO2− 1.46 and 2.55 D, respectively, make them good candidates for observation by pure rotational spectroscopy. Within the double harmonic approximation, fundamental infrared intensities have also been derived, and these results predict a relatively intense infrared vibrational spectrum in the ν3 mode of ClO2−.

Potential energy surfaces for the Pt2+H2 reaction

Potential energy surfaces for the Pt2+H2 reaction are obtained using a complete active space multiconfiguration self-consistent field (CAS-MCSCF) method followed by multireference singles+double CI (MRSDCI) calculations. Several approaches of H2 such as parallel, perpendicular, collinear, end-on with respect to Pt2 are considered. In addition, out-of-plane twist motions of hydrogens relative to the Pt–Pt bond are considered. The parallel approach was found to be most reactive in the 1A1 electronic state, which forms a cis Pt2H2 saddle point after surmounting a barrier of ∼20 kcal/mol. The saddle point thus formed spontaneously transforms to a trans Pt2H2, 1Ag ground state through an out-of-plane twist motion. The dissociation of H2 in the parallel mode of collision was found to be brought about primarily through the interaction of the d(δ) orbitals of the two Pt atoms with the H2 1σg and 1σ*u orbitals. The spin–orbit effects were studied using a relativistic CI (RCI) method and found to be significant for Pt2H2. Spin–orbit coupling was found to induce an avoided crossing. This destabilizes the Pt2H2(1Ag) molecular state with respect to the dissociated Pt2+H2. The energy separation between the Pt2H2 1Ag trans minimum and the cis saddle point was calculated at the MRSDCI level as 3 kcal/mol. We find that the reactivity of Pt2 with H2 varies as a function of electronic state and orientation.

Ozone visible photodissociation dynamics

The photolysis of ozone at 300 K in the Chappuis band has been investigated through collision-free coherent anti-Stokes Raman scattering (CARS) spectroscopy of the molecular oxygen photofragment. We have obtained the nascent electronic, vibrational, rotational, and translational energy distributions for nine photolysis wavelengths over the range 560–638 nm. The O2 photofragments are always formed in the ground (3Σ−g) state, there is no evidence for production of the excited (1Δg) state. Only a narrow range of high rotational levels are populated. The rotational distribution shifts to higher rotational states as the available energy increases. The vibrational distribution, however, is independent of photolysis wavelength. Only states v=0 to v=4 are populated, and there is a population inversion between v=2 and v=3. The average partitioning of energy among the vibrational, rotational, and translational degrees of freedom is 10%, 24%, and 66%, respectively. These results are interpreted to imply vibrationally adiabatic but rotationally impulsive dissociation dynamics. The O2 photofragment vibrational distribution is explained by Franck–Condon vibrational overlaps between O2 and the ground 1A1 electronic state of O3. Detailed consideration of the angular momentum disposal in the photodissociation indicates a strong correlation between the direction of the O2 angular momentum produced by the dissociative energy release, and the direction of the angular momentum of the O3 in-plane rotation. The correlation is such that of two energy degenerate final states, the one of higher orbital angular momentum is not produced.

Ab initio and pseudopotential calculations on the singlet and triplet states of the disilyne isomers

AbstractAb initio SCF as well as pseudopotential calculations were performed for determining equilibrium structures and relative stabilities of several disilyne isomers. For the singlet state there are only two structures, the bridged and the silavinylidene carbene, which correspond to minima on the energy hypersurface. The most stable of the six isomeric structures investigated is the bridged conformer in the 1A1 electronic state, followed by the silavinylidene carbene in the 1A1 and 3A2 electronic states. Inclusion of electron correlation by MRD‐CI calculations has no qualitative influence on the relative stabilities found in the SCF calculations.

X 3A2, a 1E, and b 1A1 electronic states of methylnitrene

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTX 3A2, a 1E, and b 1A1 electronic states of methylnitreneDavid R. Yarkony, Henry F. Schaefer III, and Stephen RothenbergCite this: J. Am. Chem. Soc. 1974, 96, 19, 5974–5977Publication Date (Print):September 1, 1974Publication History Published online1 May 2002Published inissue 1 September 1974https://doi.org/10.1021/ja00826a003RIGHTS & PERMISSIONSArticle Views67Altmetric-Citations38LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (424 KB) Get e-Alerts Get e-Alerts