Simulation of the photodetachment spectrum of HHfO- using coupled-cluster calculations

The photodetachment spectrum of HHfO? was simulated using restricted-spin coupled-cluster single-double 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

Ab initio calculations on SF2 and its low-lying cationic states: Anharmonic Franck-Condon simulation of the uv photoelectron spectrum of SF2

Geometry optimization calculations were carried out on the X (1)A(1) state of SF2 and the X B-2(1), A (2)A(1), B B-2(2), C B-2(2), D (2)A(1), and E (2)A(2) 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 2s(2)2p(6) and F 1s(2) 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 (1)A(1) 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 [Chem. Phys. 34, 287 (1978)] is excellent. Our calculations largely support assignments made by de Leeuw on the higher ionization energy bands of SF2

Ab initio calculations on low-lying electronic states of TeO2 and Franck-Condon simulation of the (1)¹B2?X¹ TeO2 absorption spectrum including anharmonicity

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-zeta quality. Equilibrium geometrical parameters, harmonic vibrational frequencies, and relative electronic energies of the (X) over tilde (1)A(1), B-1(1), B-1(2), (1)A(2), (3)A(1), B-3(1), B-3(2), and (3)A(2) states of TeO2 have been calculated. Potential energy functions (PEFs) of the (X) over tilde (1)A(1) and the (1)B-1(2) states were computed at the complete-active-space self-consistent-field multireference configuration interaction level, with a basis set of augmented-polarized valence-quadruple-zeta quality. Franck-Condon factors (FCFs) for the electronic transition between the (X) over tilde (1)A(1) and (1)B-1(2) states of TeO2 were calculated with the above-mentioned ab initio PEFs. The (1)B-1(2)<--(X) over tilde (1)A(1) 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)B-1(2) 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)B-1(2)<--(X) over tilde (1)A(1) 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)B-1(2) electronic surface with higher B-1(2) states in a region of large TeO bond length (greater than or equal to2.0 Angstrom) and OTeO bond angle (greater than or equal to135.0degrees)

Franck-Condon simulation of the single vibronic level emission spectra of HSiF and DSiF including anharmonicity

Potential energy functions (PEFs) of the (X) over tilde (1)A' and (A) over tilde (1)A" 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 in J. Chem. Phys. 114, 10728 (2001). Excellent agreement between the simulated and observed spectra was obtained for the (A) over tilde (1)A"(1,0,0)-->(X) over tilde (1)A' SVL emission of HSiF. Discrepancies between the simulated and observed spectra of the (A) over tilde (1)A"(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) over tilde (1)A' state show strong mixings between the three vibrational modes of HSi stretching, bending, and SiF stretching

Ab initio calculations on the X (2)B1 and A (2)A1 states of AsH2, and Franck-Condon simulation, including anharmonicity, of the A(0,0,0)-X single vibronic level emission spectrum of AsH2

Restricted-spin coupled-cluster single-double plus perturbative triple excitation {RCCSD(T)} calculations were carried out on the X (2)B(1) and A (2)A(1) states of AsH(2) 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 3d(10) 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 (2)A(1) state of AsH(2) relative to the X (2)B(1) state including zero-point energy correction (T(0)) is 19,954(32) cm(-1), which agrees very well with available experimental T(0) 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 (2)B(1) and A (2)A(1) states of AsH(2) 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 AsH(2) 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 AsH(2), which consist essentially of the bending (2(n)) series, suggests that there is a significant loss in intensity in the low emission energy region of the experimental spectru

Decomposition reactions of hexafluoropropylene oxide (HFPO): Rate coefficients calculated at different temperatures using ab initio and DFT reaction paths

A theoretical investigation has been carried out on the reaction mechanism and kinetics of the thermal decomposition of hexafluoropropylene oxide (HFPO), a compound of importance in fluorocarbon thin film preparation in the electronics industry. Decomposition occurs via two pathways, 1(a) to give CF2 and CF3C(O)F and 1(b) to give CF2O and CF3CF. Rate coefficients calculated for reaction 1(a) are reported over the temperature range 300–1500 K and compared with the small number of available rate coefficients at selected temperatures within this range. Rate coefficients are reported for the first time for reaction 1(b) over the temperature range 300–1500 K. The geometries of the stationary points on the potential energy surfaces have been obtained at the MP2/6-311++G(d,p) level, and the energies of selected points along the minimum energy path (MEP) have been improved at the RCCSD(T)/AVDZ and RCCSD(T)/AVTZ levels. These improved energies were extrapolated to the complete basis set limit to obtain RCCSD(T)/CBS//MP2/6-311++G(d,p) energies at each selected point on the MEP. The energies were then used in a dual-level direct dynamics method to calculate rate coefficients of the two decomposition reactions. The variational effect on the rate coefficients obtained is found to be small over the whole temperature range and tunnelling plays a small but significant role only at the lower temperatures. Comparison has been made of the computed reaction enthalpies, forward activation energies and rate coefficients computed at the RCCSD(T)/CBS//MP2/6-311++G(d,p) level with those computed with a number of different functionals and with the MP2 method. Reaction 1(a) is found to be the dominant reaction throughout the temperature range considered. Calculated rate coefficients for reaction 1(a) at the highest level used (improved canonical variational theory (ICVT) with small curvature tunnelling (SCT) with the RCCSD(T)/CBS//MP2/6-311++G(d,p) MEP) show reasonably good agreement with two recent sets of experimental values, although agreement with an older set is poor. This comparison highlights the need for more experimental rate coefficients for this thermolysis reaction over the whole temperature range considered, but particularly in the ranges 550–800 K and 1200–1500 K not currently covered by experimental measurement

The atmospherically important reaction of hydroxyl radicals with methyl nitrate: a theoretical study involving the calculation of reaction mechanisms, enthalpies, activation energies, and rate coefficients

A theoretical study, involving the calculation of reaction enthalpies and activation energies, mechanisms and rate coefficients, has been made of the reaction of hydroxyl radicals with methyl nitrate, an important process for methyl nitrate removal in the earth's atmosphere. Four reaction channels were considered:- formation of H2O + CH2ONO2, CH3OOH + NO2, CH3OH + NO3, and CH3O + HNO3 . For all channels, geometry optimization and frequency calculations were carried out at the M06-2X/6-31+G** level, while relative energies were improved at the UCCSD(T*)-F12/CBS level. The major channel is found to be the H abstraction channel, to give the products H2O + CH2ONO2. The reaction enthalpy (ΔH298KRX) of this channel is computed as -17.90 kcal.mol-1. Although the other reaction channels are also exothermic, their reaction barriers are high (> 24 kcal.mol-1) and therefore these reactions do not contribute to the overall rate coefficient in the temperature range considered (200-400 K). Pathways via three transition states have been identified for the H abstraction channel. Rate coefficients were calculated for these pathways at various levels of variational transition state theory (VTST) including tunneling. The results obtained are used to distinguish between two sets of experimental rate coefficients, measured in the temperature range 200-400K, one of which is approximately an order of magnitude greater than the other. This comparison, as well as the temperature dependence of the computed rate coefficients, shows that the lower experimental values are favoured. The implications of the results to atmospheric chemistry are discussed

Simulated photodetachment spectra of AlH2-

We have carried out high-level ab initio calculations on AlH2 and its anion, as well as Franck-Condon factor calculations, which include anharmonicity and Duschinsky rotation, to simulate the photodetachment spectrum of AlH2?, with the aim of assigning the very recently reported photodetachment spectrum of AlH2? [X. Zhang, H. Wang, E. Collins, A. Lim, G. Ganteför, B. Kiran, H. Schnöckel, B. Eichhorn, and K. Bowen, J. Chem. Phys. 138, 124303 (2013)]10.1063/1.4796200. However, our simulated spectra do not support the assignment of the reported experimental spectrum to AlH2?.<br/

A combined ab initio and Franck-Condon factor simulation study on the photdetachmnent spectrumn of the HfO2 anion

2008-2009 > Academic research: refereed > Publication in refereed journa

An ab initio study of the low-lying electronic states of YO2 and Franck-Condon simulation of the first photodetachment band of YO2

A variety of density functional theory and ab initio methods, including B3LYP, B98, BP86, CASSCF, CASSCF/RS2, CASSCF/MRCI, BD, BD(T), and CCSD(T), with ECP basis sets of up to the quintuple-zeta quality for Y, have been employed to study the X?2B2 state of YO2 and the X?1A1 state of YO2?. Providing that the Y 4s24p6 outer-core electrons are included in the correlation treatment, the RCCSD(T) method gives the most consistent results and is concluded to be the most reliable and practical computational method for YO2 and YO2?. In addition, RCCSD(T) potential energy functions (PEFs) of the X?2B2 state of YO2 and the X?1A1 state of YO2? were computed, employing the ECP28MDF_aug-cc-pwCVTZ and aug-cc-pVTZ basis sets for Y and O, respectively. Franck?Condon factors, which include allowance for Duschinsky rotation and anharmonicity, were calculated using the computed RCCSD(T) PEFs and were used to simulate the first photodetachment band of YO2?. The simulated spectrum matches very well with the corresponding experimental 355 nm photodetachment spectrum of Wu, H.; Wang, L.-S. J. Phys. Chem. A 1998, 102, 9129, confirming the reliability of the RCCSD(T) PEFs used. Further calculations on low-lying electronic states of YO2 gave Te's and Tvert's of the A?2A1, B?2B1, and C?2A2 states of YO2, as well as EAs and VDEs to these states from the X?1A1 state of YO2?. On the basis of the ab initio VDEs obtained in the present study, previous assignments of the second and third photodetachment bands of YO2? have been revised