The ?, ?* state in formaldehyde and thioformaldehyde

Grein, Friedrich; Hachey, Michel R. J.

doi:10.1002/(sici)1097-461x(1996)60:7<1661::aid-qua48>3.0.co;2-1

Cited by 12 publications

(6 citation statements)

References 21 publications

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“…1) agree qualitatively quite well with those reported by Hachey and coworkers [6,8]; however, we ®nd that the potential-energy curves participating in an avoided crossing approach each other much closer in our calculations. It is expected that these avoided crossings will turn into true crossings on variation of the remaining geometry parameters.…”

Section: Resultssupporting

confidence: 91%

“…We ®nd, however, that the n±3p y and n±3p z transitions are of similar intensity and more intense than the n±3s excitation. This observation is shared by previously reported theoretical data [5,8,11,12]. Whereas the EOM-based data [11,12] for these three states are in acceptable agreement with our MR-CISD and MR-AQCC/LRT oscillater strengths, the MR-DCI [8] and the generalized valence bond CI [5] method predict weaker transition intensities, especially for the n±3s excitation.…”

Section: Resultssupporting

confidence: 89%

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Simultaneous calculation of Rydberg and valence excited states of formaldehyde

Müller

Lischka

2001

Theoretical Chemistry Accounts: Theory, Computation, and Modeli

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The presence of low-lying Rydberg states interspersed among valence states constitutes a substantial challenge for the accurate quantum chemical calculation of electronically excited states because of the need to treat a relatively large number of states simultaneously. We present a general and ecient scheme that allows the treatment of a large number of Rydberg and valence states at the MR-CISD, MR-CISD+Q and MR-AQCC levels while using only a fraction of the size of the con®guration space as compared to a full completeactive-space reference wave function. This scheme is applied to the calculation of vertical excitations and various avoided crossings between ten Rydberg and ®ve valence singlet states of formaldehyde including transition dipole moments and oscillator strengths. Basis set eects, choice of con®guration space and size-extensivity corrections have been considered. It is found that sizeextensivity eects as computed by MR-CISD+Q and MR-AQCC play an important role especially for the description of the p±p Ã state and for avoided crossings in which this state is involved.

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Section: Resultssupporting

confidence: 91%

Section: Resultssupporting

confidence: 89%

Simultaneous calculation of Rydberg and valence excited states of formaldehyde

Müller

Lischka

2001

Theoretical Chemistry Accounts: Theory, Computation, and Modeli

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“…From the experimental side, the low-lying electronic excited states of thioformaldehyde have been studied in detail for several decades. − Thioformaldehyde possesses two low-lying nπ * states, a singlet (origin at 2.03 eV) and a triplet (at 1.80 eV) . The second triplet state, 3 ππ *, is located around 2.70 eV . After excitation to the 1 nπ * state, fluorescence with a lifetime of 70–300 μs , is typically reported.…”

Section: Introductionmentioning

confidence: 99%

The Influence of the Electronic Structure Method on Intersystem Crossing Dynamics. The Case of Thioformaldehyde

Mai

Atkins

González

2019

J. Chem. Theory Comput.

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The ability of different electronic structure methods to describe correctly intersystem crossing dynamics is evaluated, using thioformaldehyde as a test case. Mischievously, all methods considered-ranging from the multi-reference methods MR-CISD, MS-CASPT2, or SA-CASSCF, to the single-reference methods ADC(2), CC2, and TDDFT in different flavours-provide the same state ordering and energies of the low-lying singlet and triplet electronic excited states within an acceptable error of 0.2-0.3 eV. However, the outcome of the non-adiabatic simulations after excitation to the lowest S 1 ( 1 nπ * ) state are dramatically different. While MS-CASPT2, ADC(2), BP86, and PBE do not transfer population to the triplet states within 500 fs-in consonance with experimental evidence-SA-CASSCF, B3LYP, and BHHLYP predict intersystem crossing yields between 3% and 21% within the same time. The different 1 excited state dynamics can be rationalized by inspecting potential energy profiles along the C-S bond stretch mode and single-triplet energy gaps. It is found that already at a C-S bond length of 1.9Å, all the single-reference methods struggle to describe the correct asymptotic behavior of the potentials. Moreover, some methods, including SA-CASSCF, obtain incorrect 1 nπ * − 3 ππ * energy gaps, leading to compensation of errors (ADC(2), BP86, PBE), or wrong dynamics (SA-CASSCF, B3LYP, BHHLYP). Only the accurate MRCISD and MS-CASPT2 methods are able to describe the C-S bond correctly and thus able to deliver the correct potential energy surfaces and dynamics for the right reason. A correlation with the amount of Hartree-Fock exchange in the density functional and the easiness to access the 3 ππ * state from the 1 nπ * is able to explain the different behavior observed for GGA and hybrid functionals. It is thus illustrated that even in the case of a simple molecule, like CH 2 S, the sole assessment of vertical excitation energies as reliability predictors for non-adiabatic is inadequate.The reason is that ISC does not occur at the FC geometry, but rather at distorted geometries where the singlet-triplet gaps become small. Hence, a characterization of the potential energy surfaces beyond the Franck-Condon region is mandatory. IntroductionIntersystem crossing (ISC) is the radiationless transition between electronic states of different spin multiplicities, e.g., from a singlet to a triplet state. Given the involvement of ISC in many applications such as dye-sensitized solar cells, 1 organic light-emitting diodes, 2,3 or photodynamic therapy, 4,5 many studies aim at understanding this oftentimes highly complex process. 6 Only recently it has become possible to carry out nonadiabatic molecular dynamics simulations including ISC and internal conversion on the same footing. [7][8][9][10][11][12] A key ingredient in any nonadiabatic molecular dynamics simulation is the level of theory employed to calculate the electronic potential energy surfaces (PESs), on which the nuclei are moving. The aim of this work is to compare the effect that differ...

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“…In recent studies by this group, the UV and photoelectron spectra of H 2 CO − and Cl 2 CO were investigated theoretically. It has been shown how the 1 (π,π*) state of H 2 CO, not seen directly, transfers its intensity to various Rydberg states.…”

Section: Introductionmentioning

confidence: 99%

UV and Photoelectron Spectrum of Carbonyl Fluoride, F₂CO. Multireference Configuration Interaction Studies in C_2v Symmetry

Grein

1998

J. Phys. Chem. A

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Using multireference CI methods for F2CO in C 2 v symmetry, with near triple-ζ basis sets and added polarization and diffuse functions, CO, CF, and FCF potentials were calculated for four states each of 1A1, 1B1, 1B2, and 1A2 symmetry. Vertical excitation energies were obtained for six roots, both for singlet and triplet states. Also, vertical and some adiabatic ionization potentials of F2CO were calculated. System I of the UV absorption spectrum is clearly no → π*. System II, ranging from 7.02 to 7.66 eV, can only be assigned to triplet π → π*. System III is most likely no→ 3s/no → σ*. System IV, a continuum, is assigned to π → π*, on the basis of its large oscillator strength. Following calculated ionization potentials (IP), the 17.2 eV photoelectron band is assigned to 8a1 and the 16.6 eV one to 4b2. This way, up to the eighth IP, calculated and experimental values agree within 0.2 eV. The perfluoro effect has been reinvestigated. Calculated vibrational frequencies of the three lowest states of F2CO+ are used for an understanding of the vibrational structure of the photoelectron spectrum.

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The ?, ?* state in formaldehyde and thioformaldehyde

Cited by 12 publications

References 21 publications

Simultaneous calculation of Rydberg and valence excited states of formaldehyde

Simultaneous calculation of Rydberg and valence excited states of formaldehyde

The Influence of the Electronic Structure Method on Intersystem Crossing Dynamics. The Case of Thioformaldehyde

UV and Photoelectron Spectrum of Carbonyl Fluoride, F₂CO. Multireference Configuration Interaction Studies in C_2v Symmetry

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The ?, ?* state in formaldehyde and thioformaldehyde

Cited by 12 publications

References 21 publications

Simultaneous calculation of Rydberg and valence excited states of formaldehyde

Simultaneous calculation of Rydberg and valence excited states of formaldehyde

The Influence of the Electronic Structure Method on Intersystem Crossing Dynamics. The Case of Thioformaldehyde

UV and Photoelectron Spectrum of Carbonyl Fluoride, F2CO. Multireference Configuration Interaction Studies in C2v Symmetry

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Product

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UV and Photoelectron Spectrum of Carbonyl Fluoride, F₂CO. Multireference Configuration Interaction Studies in C_2v Symmetry