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The photodetachment spectrum of HHfO- was simulated using restricted-spin coupled-cluster singledouble plus perturbative triple {RCCSD(T)} calculations performed on the ground electronic states of HHfO and HHfO-, employing basis sets of up to quintuple-zeta quality. The computed RCCSD(T) electron affinity of 1.67 ± 0.02 eV at the complete basis set limit, including Hf 5s²5p6 core correlation and zero-point energy corrections, agrees well with the experimental value of 1.70 ± 0.05 eV from a recent photodetachment study [X. Li et al., J. Chem. Phys. 136, 154306 (2012)]. For the simulation, Franck-Condon factors were computed which included allowances for anharmonicity and Duschinsky rotation. Comparisons between simulated and experimental spectra confirm the assignments of the molecular carrier and electronic states involved but suggest that the experimental vibrational structure has suffered from poor signal-to-noise ratio. An alternative assignment of the vibrational structure to that suggested in the experimental work is presented. [ABSTRACT FROM AUTHOR]

The single-vibronic-level (SVL) emission spectra of HAsO and DAsO have been simulated by electronic structure/Franck-Condon factor calculations to confirm the spectral molecular carrier and to investigate the electronic states involved. Various multi-reference (MR) methods, namely, NEVPT2 (n-electron valence state second order perturbation theory), RSPT2-F12 (explicitly correlated Rayleigh-Schrodinger second order perturbation theory), and MRCI-F12 (explicitly correlated multi-reference configuration interaction) were employed to compute the geometries and relative electronic energies for the ?X¹A′ and ?ùA″ states of HAsO. These are the highest level calculations on these states yet reported. The MRCI-F12 method gives computed T0 (adiabatic transition energy including zero-point energy correction) values, which agree well with the available experimental T0 value much better than previously computed values and values computed with other MR methods in this work. In addition, the potential energy surfaces of the ?X¹A′ and ?ùA′ states of HAsO were computed using the MRCI-F12 method. Franck-Condon factors between the two states, which include anharmonicity and Duschinsky rotation, were then computed and used to simulate the recently reported SVL emission spectra of HAsO and DAsO [R. Grimminger and D. J. Clouthier, J. Chem. Phys. 135, 184308 (2011)]. Our simulated SVL emission spectra confirm the assignments of the molecular carrier, the electronic states involved, and the vibrational structures observed in the SVL emission spectra but suggest a loss of intensity in the reported experimental spectra at the low emission energy region almost certainly due to a loss of responsivity near the cutoff region (~800 nm) of the detector used. Computed and experimentally derived re (equilibrium) and/or r0 {the (0,0,0) vibrational level} geometries of the two states of HAsO are discussed. [ABSTRACT FROM AUTHOR]

The reaction, BrO + HO2 → HOBr + O2, is exothermic and can produce O2 in both its ground state (X~;3∑g−) and its first excited state (ã1Δg). As a result, this reaction can proceed on both a singlet and a triplet potential energy surface. Recently, Tsona, Tang and Du published a paper entitled "Impact of water on the BrO + HO2 gas-phase reaction: mechanism, kinetics and products (Phys. Chem. Chem. Phys. 2019, 21, 20296–203072). The results of this work showed significant differences from those published earlier on this reaction by Chow et al. (Phys. Chem. Chem. Phys. 2016, 18, 30554–30569). Further calculations performed in this present work, combined with higher level calculations published by Chow et al. (Phys. Chem. Chem. Phys. 2016, 18, 30554–30569), demonstrate that the work of Tsona et al. is flawed because the integration grid size used in their lowest singlet and triplet calculations is too small, and a closed-shell wavefunction, rather than an open-shell wavefunction, has been used for the singlet surface. The major conclusion in the work of Tsona et al. that the lowest singlet and triplet channels are barrierless is shown to be incorrect. Also, the computed rate coefficients of Tsona et al. showed a positive temperature dependence, which is inconsistent with the experimentally observed negative temperature dependence, whereas the singlet rate coefficients computed by Chow et al. (Phys. Chem. Chem. Phys. 2016, 18, 30554–30569) showed a negative temperature dependence consistent with experiment. [ABSTRACT FROM AUTHOR]

We have computed the potential energy surfaces of the X1A' and A1A" states of HPS using the explicitly correlated multi-reference configuration interaction (MRCI-F12) method, and Franck-Condon factors between the two states, which include anharmonicity and Duschinsky rotation, with the aim of testing the assignment of the recently reported single-vibronic-level (SVL) emission spectrum of HPS [R. Grimminger, D. J. Clouthier, R. Tarroni, Z. Wang, and T. J. Sears, J. Chem. Phys. 139, 174306 (2013)]. These are the highest level calculations on these states yet reported. It is concluded that our spectral simulation supports the assignments of the molecular carrier, the electronic states involved and the vibrational structure of the experimental laser induced fluorescence, and SVL emission spectra proposed by Grimminger et al. [J. Chem. Phys. 139, 174306 (2013)]. However, there remain questions unanswered regarding the relative electronic energies of the two states and the geometry of the excited state of HPS. [ABSTRACT FROM AUTHOR]

The reaction of hydroxymethyl hydroperoxide (HMHP, HOCH2OOH) with the simplest Criegee intermediate, CH2OO, has been examined using quantum chemical methods with transition state theory. Geometry optimization and IRC calculations were performed using the M06-2X, MN15-L, and B2PLYP-D3 functionals in conjunction with the aug-cc-pVTZ basis set. Single point energy calculations using QCISD(T) and BD(T) with the same basis set have been performed to determine the energy of reactants, reactive complexes, transition states, and products. Rate coefficients have been obtained using variational transition state theory. The addition of CH2OO on the three different oxygen atoms in HMHP has been considered and the ether oxide forming channel, CH2OO + HOCH2OOH → HOCH2O(O)CH2OOH (channel 2), is the most favorable. The best computed standard enthalpy of reaction (ΔH RX298K) and zero-point corrected barrier height are −20.02 and −6.33 kcal mol−1, respectively. The reaction barrier is negative and our results suggest that both the inner and outer transition states contribute to the corresponding overall reactive flux in the tropospheric temperature range (220 K to 320 K). A two-transition state model has been used to obtain reliable rate coefficients at the high-pressure limit. The pressure-dependent rate coefficient calculations using the SS-QRRK theory have shown that this channel is pressure-dependent. Moreover, our investigation has shown that the ether oxide formed may rapidly react with SO2 at 298 K to form SO3, which can, in turn, react with water to form atmospheric H2SO4. A similar calculation has been conducted for the reaction of HMHP with OH, suggesting that the titled reaction may be a significant sink of HMHP. Therefore, the reaction between CH2OO and HOCH2OOH could be an indirect source for generating atmospheric H2SO4, which is crucial to the formation of clouds, and it might relieve global warming. [ABSTRACT FROM AUTHOR]

Geometry optimization and harmonic vibrational frequency calculations have been carried out on the X2A′ state of P2H and the X1A′ state of P2H- using the restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] and explicitly correlated unrestricted-spin coupled-cluster single-double plus perturbative triple excitation [UCCSD(T)-F12x] methods. For RCCSD(T) calculations, basis sets of up to the augmented correlation-consistent polarized valence quintuple-zeta (aug-cc-pV5Z) quality were employed, and contributions from extrapolation to the complete basis set limit and from core correlation of the P 2s22p6 electrons were also included. For UCCSD(T)-F12x calculations, different atomic orbital basis sets of triple-zeta quality with different associated complementary auxiliary basis sets and different geminal Slater exponents were used. When the P 2s22p6 core electrons were correlated in these F12x calculations, appropriate core-valence basis sets were employed. In addition, potential energy functions (PEFs) of the X2A′ state of P2H and the X1A′ state of P2H- were computed at different RCCSD(T) and UCCSD(T)-F12x levels, and were used in variational calculations of anharmonic vibrational wavefunctions, which were then utilized to calculate Franck-Condon factors (FCFs) between these two states, employing a method which includes allowance for anharmonicity and Duschinsky rotation. The photodetachment spectrum of P2H- was then simulated using the computed FCFs. Simulated spectra obtained using the RCCSD(T)/aug-cc-pV5Z and UCCSD(T)-F12x(x = a or b)/aug-cc-pCVTZ PEFs are compared and found to be essentially identical. Based on the computed FCFs, a more detailed assignment of the observed vibrational structure than previously reported, which includes 'hot bands,' has been proposed. Comparison between simulated and available experimental spectra has been made, and the currently most reliable sets of equilibrium geometrical parameters for P2H and its anion have been derived. The photodetachment spectrum of P2D, yet to be recorded, has also been simulated. [ABSTRACT FROM AUTHOR]

Restricted-spin coupled-cluster single-double plus perturbative triple excitation {RCCSD(T)} calculations were carried out on the X 2B1 and A 2A1 states of AsH2 employing the fully relativistic small-core effective core potential (ECP10MDF) for As and basis sets of up to the augmented correlation-consistent polarized valence quintuple-zeta (aug-cc-pV5Z) quality. Minimum-energy geometrical parameters and relative electronic energies were evaluated, including contributions from extrapolation to the complete basis set limit and from outer core correlation of the As 3d10 electrons employing additional tight 4d3f2g2h functions designed for As. In addition, simplified, explicitly correlated CCSD(T)-F12 calculations were also performed employing different atomic orbital basis sets of up to aug-cc-pVQZ quality, and associated complementary auxiliary and density-fitting basis sets. The best theoretical estimate of the relative electronic energy of the A 2A1 state of AsH2 relative to the X 2B1 state including zero-point energy correction (T0) is 19 954(32) cm-1, which agrees very well with available experimental T0 values of 19 909.4531(18) and 19 909.4910(17) cm-1 obtained from recent laser induced fluorescence and cavity ringdown absorption spectroscopic studies. In addition, potential energy functions (PEFs) of the X 2B1 and A 2A1 states of AsH2 were computed at different RCCSD(T) and CCSD(T)-F12 levels. These PEFs were used in variational calculations of anharmonic vibrational wave functions, which were then utilized to calculate Franck–Condon factors (FCFs) between these two states, using a method which includes allowance for anharmonicity and Duschinsky rotation. The A(0,0,0)-X single vibronic level (SVL) emission spectrum of AsH2 was simulated using these computed FCFs. Comparison between simulated and available experimental vibrationally resolved spectra of the A(0,0,0)-X SVL emission of AsH2, which consist essentially of the bending (2n) series, suggests that there is a significant loss in intensity in the low emission energy region of the experimental spectrum. [ABSTRACT FROM AUTHOR]

Minimum-energy geometries and relative electronic energies of the X 1A′ and à 1A″ states of HPO have been computed employing the coupled-cluster single-double plus perturbative triple excitations {RCCSD(T)} and/or complete-active-space self-consistent-field (CASSCF) multireference internally contracted configuration interaction (MRCI) methods with basis sets of up to the augmented correlation-consistent polarized-valence quintuple-zeta (aug-cc-pV5Z) quality. In addition, RCCSD(T)/aug-cc-pVQZ and CASSCF/MRCI/aug-cc-pVQZ potential energy functions, anharmonic vibrational wave functions, and energies involving all three vibrational modes for both electronic states of HPO and DPO, and Franck-Condon factors between the two electronic states, which allow for Duschinsky rotation and anharmonicity, were computed. Computed Franck-Condon factors were then used to simulate single vibronic level (SVL) emission spectra recently reported by Tackett and Clouthier [J. Chem. Phys. 117, 10604 (2002)]. Excellent agreement between the simulated and observed spectra was obtained for the à 1A″(1,0,0)→X 1A′ SVL emission of HPO and DPO, when the best estimated ab initio geometries of the two states, which include contributions from core correlation and extrapolation to the complete basis set limit, were used in the simulation, suggesting that the best estimated ab initio geometry of the à 1A″ state of HPO, particularly the bond angle of 94.5°, is more reliable than the available experimentally derived geometry. A discussion on the geometrical parameters derived from rotational constants obtained from the rotational analysis of a high-resolution spectrum and from Franck-Condon simulation of the vibrational structure of an electronic spectrum is given. [ABSTRACT FROM AUTHOR]

Geometry optimization and harmonic vibrational frequency calculations have been carried out on the low-lying singlet and triplet electronic states of the antimony dioxide anion (SbO2-) employing a variety of ab initio methods. Both large-core and small-core relativistic effective core potentials were used for Sb in these calculations, together with valence basis sets of up to augmented correlation-consistent polarized-valence quintuple-zeta (aug-cc-pV5Z) quality. The ground electronic state of SbO2- is determined to be the X 1A1 state, with the ã 3B1 state, calculated to be ∼48 kcal mole-1 (2.1 eV) higher in energy. Further calculations were performed on the X 2A1, Ã 2B2, and B 2A2 states of SbO2 with the aim to simulating the photodetachment spectrum of SbO2-. Potential energy functions (PEFs) of the X 1A1 state of SbO2- and the X 2A1, Ã 2B2, and B 2A2 states of SbO2 were computed at the complete-active-space self-consistent-field multireference internally contracted configuration interaction level with basis sets of augmented correlation-consistent polarized valence quadruple-zeta quality. Anharmonic vibrational wave functions obtained from these PEFs were used to compute Franck-Condon factors between the X 1A1 state of SbO2- and the X 2A1, Ã 2B2, and B 2A2 states of SbO2, which were then used to simulate the photodetachment spectrum of SbO2-, which is yet to be recorded experimentally. [ABSTRACT FROM AUTHOR]

Minimum-energy geometries, harmonic vibrational frequencies, and relative electronic energies of some low-lying singlet and triplet electronic states of stannous dichloride, SnCl2, have been computed employing the complete-active-space self-consistent-field/multireference configuration interaction (CASSCF/MRCI) and/or restricted-spin coupled-cluster single-double plus perturbative triple excitations [RCCSD(T)] methods. The small core relativistic effective core potential, ECP28MDF, was used for Sn in these calculations, together with valence basis sets of up to augmented correlation-consistent polarized-valence quintuple-zeta (aug-cc-pV5Z) quality. Effects of outer core electron correlation on computed geometrical parameters have been investigated, and contributions of off-diagonal spin-orbit interaction to relative electronic energies have been calculated. In addition, RCCSD(T) or CASSCF/MRCI potential energy functions of the X 1A1, ã 3B1, and B 1B1 states of SnCl2 have been computed and used to calculate anharmonic vibrational wave functions of these three electronic states. Franck-Condon factors between the X 1A1 state, and the ã 3B1 and B 1B1 states of SnCl2, which include anharmonicity and Duschinsky rotation, were then computed, and used to simulate the ã-X and B-X absorption and corresponding single-vibronic-level emission spectra of SnCl2 which are yet to be recorded. It is anticipated that these simulated spectra will assist spectroscopic identification of gaseous SnCl2 in the laboratory and/or will be valuable in in situ monitoring of SnCl2 in the chemical vapor deposition of SnO2 thin films in the semiconductor gas sensor industry by laser induced fluorescence and/or ultraviolet absorption spectroscopy, when a chloride-containing tin compound, such as tin dichloride or dimethyldichlorotin, is used as the tin precursor. [ABSTRACT FROM AUTHOR]

Geometry optimization calculations were carried out on the X 1A1 state of SCl2 and the X 2B1, Ã 2B2, B 2A1, C 2A1, D 2A2, and E 2B2 states of SCl2+ at the restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] level with basis sets of up to the augmented correlation-consistent polarized quintuple-zeta [aug-cc-pV(5+d)Z] quality. Effects of core electron correlation, basis set extension to the complete basis set limit, and relativistic contributions on computed minimum-energy geometrical parameters and/or relative electronic energies were also investigated. RCCSD(T) potential energy functions (PEFs) were calculated for the X 1A1 state of SCl2 and the low-lying states of SCl2+ listed above employing the aug-cc-pV(5+d)Z basis set. Anharmonic vibrational wave functions of these neutral and cationic states of SCl2, and Franck-Condon (FC) factors of the lowest four one-electron allowed neutral photoionizations were computed employing the RCCSD(T)/aug-cc-pV(5+d)Z PEFs. Calculated FC factors with allowance for the Duschinsky rotation and anharmonicity were used to simulate the first four photoelectron (PE) bands of SCl2. The agreement between simulated and observed He I PE spectra reported by Colton et al. [J. Electron Spectrosc. Relat. Phenom. 3, 345 (1974)] and Solouki et al. [Chem. Phys. Lett. 26, 20 (1974)] is excellent. However, our FC spectral simulations indicate that the first observed vibrational component in the first PE band of SCl2 is a “hot” band arising from the SCl2+X 2B1(0,0,0)←SCl2X 1A1(1,0,0) ionization. Consequently, the experimental adiabatic ionization energy of SCl2 is revised to 9.55±0.01 eV, in excellent agreement with results obtained from state-of-the-art ab initio calculations in this work. [ABSTRACT FROM AUTHOR]

Geometry optimization calculations were carried out on the X 1A1 state of SF2 and the X 2B1, Ã 2A1, B 2B2, C 2B2, D 2A1, and E 2A2 states of SF2+ employing the restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] method and basis sets of up to the augmented correlation-consistent polarized quintuple-zeta [aug-cc-pV(5+d)Z] quality. Effects of core electron (S 2s22p6 and F 1s2 electrons) correlation and basis set extension to the complete basis set limit on the computed minimum-energy geometries and relative electronic energies (adiabatic and vertical ionization energies) were investigated. RCCSD(T) potential energy functions (PEFs) were calculated for the X 1A1 state of SF2 and the low-lying states of SF2+ listed above employing the aug-cc-pV(5+d)Z and aug-cc-pV5Z basis sets for S and F, respectively. Anharmonic vibrational wave functions of these neutral and cationic states of SF2, and Franck-Condon (FC) factors of the lowest four one-electron allowed neutral photoionizations were computed employing the RCCSD(T) PEFs. Calculated FC factors with allowance for Duschinsky rotation and anharmonicity were used to simulate the first four photoelectron bands of SF2. The agreement between the simulated and observed first bands in the He I photoelectron spectrum reported by de Leeuw et al. [Chem. Phys. 34, 287 (1978)] is excellent. Our calculations largely support assignments made by de Leeuw et al. on the higher ionization energy bands of SF2. [ABSTRACT FROM AUTHOR]

Geometry optimization calculations were carried out on the X 1A1 state of SF2 and the X 2B1, Ã 2A1, B 2B2, C 2B2, D 2A1, and E 2A2 states of SF2+ employing the restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] method and basis sets of up to the augmented correlation-consistent polarized quintuple-zeta [aug-cc-pV(5+d)Z] quality. Effects of core electron (S 2s22p6 and F 1s2 electrons) correlation and basis set extension to the complete basis set limit on the computed minimum-energy geometries and relative electronic energies (adiabatic and vertical ionization energies) were investigated. RCCSD(T) potential energy functions (PEFs) were calculated for the X 1A1 state of SF2 and the low-lying states of SF2+ listed above employing the aug-cc-pV(5+d)Z and aug-cc-pV5Z basis sets for S and F, respectively. Anharmonic vibrational wave functions of these neutral and cationic states of SF2, and Franck-Condon (FC) factors of the lowest four one-electron allowed neutral photoionizations were computed employing the RCCSD(T) PEFs. Calculated FC factors with allowance for Duschinsky rotation and anharmonicity were used to simulate the first four photoelectron bands of SF2. The agreement between the simulated and observed first bands in the He I photoelectron spectrum reported by de Leeuw et al. [Chem. Phys. 34, 287 (1978)] is excellent. Our calculations largely support assignments made by de Leeuw et al. on the higher ionization energy bands of SF2. [ABSTRACT FROM AUTHOR]

Geometry optimization calculations were carried out on the X 1A1 state of SCl2 and the X 2B1, Ã 2B2, B 2A1, C 2A1, D 2A2, and E 2B2 states of SCl2+ at the restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] level with basis sets of up to the augmented correlation-consistent polarized quintuple-zeta [aug-cc-pV(5+d)Z] quality. Effects of core electron correlation, basis set extension to the complete basis set limit, and relativistic contributions on computed minimum-energy geometrical parameters and/or relative electronic energies were also investigated. RCCSD(T) potential energy functions (PEFs) were calculated for the X 1A1 state of SCl2 and the low-lying states of SCl2+ listed above employing the aug-cc-pV(5+d)Z basis set. Anharmonic vibrational wave functions of these neutral and cationic states of SCl2, and Franck-Condon (FC) factors of the lowest four one-electron allowed neutral photoionizations were computed employing the RCCSD(T)/aug-cc-pV(5+d)Z PEFs. Calculated FC factors with allowance for the Duschinsky rotation and anharmonicity were used to simulate the first four photoelectron (PE) bands of SCl2. The agreement between simulated and observed He I PE spectra reported by Colton et al. [J. Electron Spectrosc. Relat. Phenom. 3, 345 (1974)] and Solouki et al. [Chem. Phys. Lett. 26, 20 (1974)] is excellent. However, our FC spectral simulations indicate that the first observed vibrational component in the first PE band of SCl2 is a “hot” band arising from the SCl2+X 2B1(0,0,0)←SCl2X 1A1(1,0,0) ionization. Consequently, the experimental adiabatic ionization energy of SCl2 is revised to 9.55±0.01 eV, in excellent agreement with results obtained from state-of-the-art ab initio calculations in this work. [ABSTRACT FROM AUTHOR]

Geometry optimization and harmonic vibrational frequency calculations have been carried out on the low-lying doublet electronic states of antimony dioxide (SbO2) employing a variety of ab initio methods, including the complete active space self-consistent field/multireference configuration interaction and the RCCSD(T) methods. Both large and small core relativistic effective core potentials were used for Sb in these calculations, together with valence basis sets of up to aug-cc-pV5Z quality. Contributions from outer core correlation and off-diagonal spin-orbit interaction to relative electronic energies have been calculated. The ground electronic state of SbO2 is determined to be the X 2A1 state, as is the case for dioxides of other lighter group 15 p-block (or group VA) elements. However, the à 2B2 and B 2A2 states are estimated to be only 4.1 and 10.7 kcal/mole above the X 2A1 state, respectively, at the complete basis set limit. Reliable vertical excitation energies from the X 2A1 state to low-lying excited states of SbO2 have been computed with a view to assist future spectral assignments of the absorption and/or laser-induced fluorescence spectra of SbO2, when they become available. [ABSTRACT FROM AUTHOR]

Ab initio calculations have been carried out on low-lying singlet and triplet states of TeO2 at different levels of theory with basis sets of up to the augmented-polarized valence-quintuple-ζ quality. Equilibrium geometrical parameters, harmonic vibrational frequencies, and relative electronic energies of the X 1A1, 1B1, 1B2, 1A2, 3A1, 3B1, 3B2, and 3A2 states of TeO2 have been calculated. Potential energy functions (PEFs) of the X 1A1 and the (1)1B2 states were computed at the complete-active-space self-consistent-field multireference configuration interaction level, with a basis set of augmented-polarized valence-quadruple-ζ quality. Franck-Condon factors (FCFs) for the electronic transition between the X 1A1 and (1)1B2 states of TeO2 were calculated with the above-mentioned ab initio PEFs. The (1)1B2←X 1A1 absorption spectrum of TeO2 was simulated employing the computed FCFs, which include Duschinsky rotation and anharmonicity, and compared with the recently published laser-induced fluorescence (LIF) spectrum of Hullah and Brown [J. Mol. Spectrosc. 200, 261 (2000)]. The ab initio results and spectral simulation reported here confirm the upper electronic state involved in the LIF spectrum to be the (1)1B2 state of TeO2 and also confirm the vibrational assignments of Hullah and Brown. However, our simulated spectrum suggests that the reported LIF spectrum from 345 to 406 nm represents only a portion of the full (1)1B2←X 1A1 absorption spectrum of TeO2, which extends from ca. 406 to 300 nm. Another dye other than the two used by Hullah and Brown is required to cover the 345–300 nm region of the LIF band. Ab initio calculations show strong configuration mixing of the (1)1B2 electronic surface with higher 1B2 states in a region of large TeO bond length (>=2.0 Å) and OTeO bond angle (>=135.0°). © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] potential energy functions (PEFs) were calculated for the X 2A″ and à 2A′ states of HPCl employing the augmented correlation-consistent polarized-valence-quadruple-ζ (aug-cc-pVQZ) basis set. Further geometry optimization calculations were carried out on both electronic states of HPCl at the RCCSD(T) level with all electron and quasirelativistic effective core potential basis sets of better than the aug-cc-pVQZ quality, and also including some core electrons, in order to obtain more reliable geometrical parameters and relative electronic energy of the two states. Anharmonic vibrational wave functions of the two states of HPCl and DPCl, and Franck-Condon (FC) factors of the à 2A′-X 2A″ transition were computed employing the RCCSD(T)/aug-cc-pVQZ PEFs. Calculated FC factors with allowance for Duschinsky rotation and anharmonicity were used to simulate the single-vibronic-level (SVL) emission spectra of HPCl and DPCl reported by Brandon et al. [J. Chem. Phys. 119, 2037 (2003)] and the chemiluminescence spectrum reported by Bramwell et al. [Chem. Phys. Lett. 331, 483 (2000)]. Comparison between simulated and observed SVL emission spectra gives the experimentally derived equilibrium geometry of the à 2A′ state of HPCl of re(PCl)=2.0035±0.0015 Å, θe=116.08±0.60°, and re(HP)=1.4063±0.0015 Å via the iterative Franck-Condon analysis procedure. Comparison between simulated and observed chemiluminescence spectra confirms that the vibrational population distribution of the à 2A′ state of HPCl is non-Boltzmann, as proposed by Baraille et al. [Chem. Phys. 289, 263 (2003)]. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Broadband ultraviolet absorption spectroscopy has been used to determine CF2 densities in a plasma etch reactor used for industrial wafer processing, using the CF2 à 1B1&Xtilde; 1A1 absorption spectrum. Attempts to fit the experimental spectra using previously published Frank-Condon factors gave poor results, and values for the higher vibrational levels of the à state [(0, v2,0), with v2'>61 from the ground state were missing; hence new values were calculated. These were computed for transitions between low-lying vibrational levels of CF2&Xtilde;¹A1 to vibrational levels of CF2ùB1(v'1,v'2,0) up to high values of the vibrational quantum numbers using high level ab initio calculations combined with an anharmonic Franck Condon factor method. The Franck Condon factors were used to determine the absorption cross sections of CF2 at selected wavelenghts, which in turn were used to calculate number densities from the experimental spectra. Number densities of CF2 have been determined in different regions of the plasma, including the center of the plasma and outside the plasma volume, and CF2 rotational temperatures and vibrational energy distributions were estimated. For absorption spectra obtained outside the confined plasma volume, the CF2 density was determined as (0.39 ±0.08) x 1013 molecule cm ³ and the vibrational and rotational temperatures were determined as 303 and 350 k, respectively. In the center of the plasma reactor, the CF2 density is estimated as (3.0 ±) x 1013 molecule cm³ with Trot ≈ 500K. The fitted vibrational distribution in the CF2 ground state corresponds to two Boltzmann distributions with Tvib≈ 300 and Tvib ≈ 1000K, indicating that CF2 molecules are initially produced highly vibrationally excited, but are partially relaxed in the plasma by collision. [ABSTRACT FROM AUTHOR]

Potential energy functions (PEFs) of the X [sup 1]A[sup ′] and à [sup 1]A[sup ″] states of HSiF have been computed using the coupled-cluster single-double plus perturbative triple excitations and complete-active-space self-consistent-field multireference internally contracted configuration interaction methods, respectively, employing augmented correlation-consistent polarized-valence quadruple-zeta basis sets. For both electronic states of HSiF and DSiF, anharmonic vibrational wavefunctions and energies of all three modes have been calculated variationally with the ab initio PEFs and using Watson’s Hamiltonian for nonlinear molecules. Franck–Condon factors between the two electronic states, allowing for Duschinsky rotation, were computed using the calculated anharmonic vibrational wavefunctions. These Franck–Condon factors were used to simulate the single vibronic level (SVL) emission spectra recently reported by Hostutler et al. in J. Chem. Phys. 114, 10728 (2001). Excellent agreement between the simulated and observed spectra was obtained for the à [sup 1]A[sup ″](1,0,0)→X [sup 1]A[sup ′] SVL emission of HSiF. Discrepancies between the simulated and observed spectra of the à [sup 1]A[sup ″](0,1,0) and (1,1,0) SVL emissions of HSiF have been found. These are most likely, partly due to experimental deficiencies and, partly to inadequacies in the ab initio levels of theory employed in the calculation of the PEFs. Based on the computed Franck–Condon factors, minor revisions of previous vibrational assignments are suggested. The calculated anharmonic wave functions of higher vibrational levels of the X [sup 1]A[sup ′] state show strong mixings between the three vibrational modes of HSi stretching, bending, and SiF stretching. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Metal-cyclen complexes have a number of important applications. However, the coordination chemistry between metal ions and cyclen-based macrocycles is much less well studied compared to their metal ion-crown ether analogues. This work, which makes a contribution to address this imbalance by studying complex ions of the type [M(Me4cyclen)(L)]+, was initiated by results of an experimental study which prepared some Group 1 metal cyclen complexes, namely [Li(Me4cyclen)(H2O)][BArF] and [Na(Me4cyclen)(THF)][BArF] and obtained their X-ray crystal structures [J. M. Dyke, W. Levason, M. E. Light, D. Pugh, G. Reid, H. Bhakhoa, P. Ramasami, and L. Rhyman, Dalton Trans., 2015, 44, 13853]. The lowest [M(Me4cyclen)(L)]+ minimum energy structures (M = Li, Na, K, and L = H2O, THF, DEE, MeOH, DCM) are studied using density functional theory (DFT) calculations. The geometry of each [M(Me4cyclen)(L)]+ structure and, in particular, the conformation of L are found to be mainly governed by steric hindrance which decreases as the size of the ionic radius increases from Li+→ Na+→ K+. Good agreement of computed geometrical parameters of [Li(Me4cyclen)(H2O)]+ and [Na(Me4cyclen)(THF)]+ with the corresponding geometrical parameters derived from the crystal structures [Li(Me4cyclen)(H2O)]+[BArF]− and [Na(Me4cyclen)(THF)]+[BArF]− is obtained. Bonding analysis indicates that the stability of the [M(Me4cyclen)(L)]+ structures originates mainly from ionic interaction between the Me4cyclen/L ligands and the M+ centres. The experimental observation that [M(Me4cyclen)(L)]+[BArF]− complexes could be prepared in crystalline form for M+ = Li+ and Na+, but that experiments aimed at synthesising the corresponding K+, Rb+, and Cs+ complexes failed resulting in formation of [Me4cyclenH][BArF] is investigated using DFT and explicitly correlated calculations, and explained by considering production of [Me4cyclenH]+ by a hydrolysis reaction, involving traces of water, which competes with [M(Me4cyclen)(L)]+ formation. [Me4cyclenH]+ formation dominates for M+ = K+, Rb+, and Cs+ whereas formation of [M(Me4cyclen)(L)]+ is energetically favoured for M+ = Li+ and Na+. The results indicate that the number and type of ligands, play a key role in stabilising the [M(Me4cyclen)]+ complexes and it is hoped that this work will encourage experimentalists to prepare and characterise other [M(Me4cyclen)(L)]+ complexes. [ABSTRACT FROM AUTHOR]

A theoretical study has been made of the BrO + HO2 reaction, a radical–radical reaction which contributes to ozone depletion in the atmosphere via production of HOBr. Reaction enthalpies, activation energies and mechanisms have been determined for five reaction channels. Also rate coefficients have been calculated, in the atmospherically important temperature range 200–400 K, for the two channels with the lowest activation energies, both of which produce HOBr: (R1a) HOBr(X1A′) + O2(X3Σ−g) and (R1b) HOBr(X1A′) + O2(a1Δg). The other channels considered are: (R2) BrO + HO2→ HBr + O3, (R3) BrO + HO2→ OBrO + OH and (R4) BrO + HO2→ BrOO + OH. For all channels, geometry optimization and frequency calculations were carried out at the M06-2X/AVDZ level, while relative energies of the stationary points on the reaction surface were improved at a higher level (BD(TQ)/CBS or CCSD(T)/CBS). The computed standard reaction enthalpies (ΔHRX298K) for channels (R1a), (R1b), (R2), (R3) and (R4) are −47.5, −25.0, −4.3, 14.9 and 5.9 kcal mol−1, and the corresponding computed activation energies (ΔE) are 2.53, −3.07, 11.83, 35.0 and 37.81 kcal mol−1. These values differ significantly from those obtained in earlier work by Kaltsoyannis and Rowley (Phys. Chem. Chem. Phys., 2002, 4, 419–427), particularly for channel (R1b), and reasons for this are discussed. In particular, the importance of obtaining an open-shell singlet wavefunction, rather than a closed-shell singlet wavefunction, for the transition state of this channel is emphasized. Rate coefficient calculations from computed potential energy surfaces were made for BrO + HO2 for the first time. Although channel (R1a) is the most exothermic, channel (R1b) has the lowest barrier height, which is negative (at −3.07 kcal mol−1). Most rate coefficient calculations were therefore made for (R1b). A two transition state model has been used, involving an outer and an inner transition state. The inner transition state was found to be the major bottleneck of the reaction with the outer transition state having essentially no effect on the overall rate coefficient (k) in the temperature range considered. Studying the entropy, enthalpy and free energy of activation of this channel as a function of temperature shows that the main contributor to the magnitude of ln k at a selected temperature is the entropy term (ΔS#/kB) whereas the temperature dependence of ln k is determined mainly by the enthalpy term (−ΔH#/kBT). This compares with reactions with positive barrier heights where the enthalpy term makes a bigger contribution to ln k. Comparison of the computed rate coefficients with available experimental values shows that the computed values have a negative temperature dependence, as observed experimentally, but are too low by approximately an order of magnitude at any selected temperature in the range 200–400 K. [ABSTRACT FROM AUTHOR]

Background: Cycloartane triterpenoids exhibited anticancer efects. This study aims to identify any potential novel anticancer cycloartane triterpenoids from Cimicifuga foetida L. rhizome (Sheng ma) and the mode of actions. Methods: Cycloartane triterpenoids were isolated from the C. foetida rhizome by a series of column chromatography and identiied by IR, MS and NMR. Their anticancer efects on several human cancer cell lines, MCF-7, HepG2, HepG2/ ADM, HeLa, and PC3, and normal human mammary epithelial cells MCF10A were investigated by colony formation and MTT assays. Morphological analysis of apoptosis induction was performed by acridine orange/ethidium bromide dual-staining and Hoechst 33258 nuclear staining. The cell-cycle proile and annexin V staining were evaluated by low cytometry. Apoptosis were investigated by measuring changes in mitochondrial membrane potential and analyzing expression of cell cycle- and apoptosis-related proteins in MCF-7 cells by Western blotting. Results: A novel cycloartane triterpenoid, 25-O-acetyl-7,8-didehydrocimigenol-3-O-β-D-(2-acetyl)xylopyranoside (ADHC-AXpn), together with the known 7,8-didehydrocimigenol-3-O-β-d-xylopyranoside (DHC-Xpn) were isolated. MCF-7 growth was signiicantly inhibited by ADHC-AXpn in a dose- and time-dependent manner (IC50 : 27.81 µM at 48 h; P = 0.004 vs. control at 25 µM for 48 h treatment), and ADHC-AXpn was selectively cytotoxic for cancerous cells (MCF-7, HepG2/ADM, HepG2 and HELA cells) based on its higher IC50 values for normal cells MCF10A (IC50 : 78.63 µM at 48 h) than for tumor cells. In MCF-7 cells, ADHC-AXpn induced G2/M cell cycle arrest by mediating cyclin-B1, and CDK1 and its phosphorylation; and induced apoptosis through the mitochondrial-mediated apoptotic pathway, with inhibition of Akt activation. As ADHC-AXpn suppressed phosphorylation of ERK1/2, Raf and Akt proteins in MCF-7 cells, its apoptotic efect might be associated with Raf/MEK/ERK signaling and Akt activation. Conclusions: ADHC-AXpn signiicantly suppressed the growth of MCF-7 cells, induced mitochondrial apoptosis and cell-cycle arrest, and inhibited Raf/MEK/ERK signaling pathway and Akt phosphorylation. [ABSTRACT FROM AUTHOR]