Configuration interaction studies on the S2surface of H2CO: 21A′(σ, π*/π, π*) as perturber of 11B2(n, 3s)

Hachey, Michel R. J.; Bruna, Pablo J.; Grein, Friedrich

doi:10.1039/ft9949000683

Cited by 21 publications

(30 citation statements)

References 37 publications

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“…The spectroscopic relevance of a double minimum on the S 2 surface revealed by these calculations has already been discussed in our previous paper. 36 The present report gives the results for the singlet states of planar H2CO. Due to the large amount of material, part of the comparison between theoretical and experimental data is published ~eparately.~~ Singlet states of nonplanar H F O , as well as the properties of triplet and quintet states, will be reported elsewhere.38 to H2CO' .…”

Section: + -mentioning

confidence: 96%

“…It is worth noting that the lowest virtual a' MO of HCO also has a 3s-a*cH mixed compositi~n.~~ The hydrogenic contribution to 3s explains the polarity reversal accompanying the excitation 11B2(n,3s) + %'A1 of H2CO: a dipole moment p of -2.42 D (H2C+O-) for %IAl changes to +3.45 D (H2C-O+) for 11B2. 36 The 2'B2(n,3p2) state has a minimum at R = 2.298 bohrs. As R(C0) increases, the potential curves of the 'Bz(n,3d) states are heavily distorted by mixing with n,o*co.…”

Section: Co Stretch Potential Curves For Valence and Rydberg Statmentioning

confidence: 99%

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Spectroscopy of Formaldehyde. 1. Ab Initio Studies on Singlet Valence and Rydberg States of Planar H2CO, with Emphasis on 1(.pi.,.pi.) and 1(.sigma.,.pi.)

Hachey¹,

Bruna²,

Grein³

1995

J. Phys. Chem.

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CO stretching potentials were obtained by ab initio multireference CI calculations for singlet valence and Rydberg states of H2CO in CzV symmetry. Within the Franck-Condon region, the valence states 'Bl(o,n*) and 'Al(n,n*) cross all members of the n -Ryd series as well as 'Bl(n,3s). The structures of the absorption bands are therefore extensively altered by vibronic mixing, intensity borrowing, and predissociative interactions.This explains why the n -Ryd bands are observed to be vibrationally more complex and of higher intensity than expected. Since lA~(n,n*) becomes the ground state at large R(CO), n,n* is capable of coupling all 'AI Rydberg states with the ground state, which dissociates to CH2 + 0 fragments at 7.64 eV. Thus, the observed absorption continuum above 7.5 eV is attributable to predissociating interactions. In the vertical region, the 'Al(n,n*) valence state lies at 9.6 eV and exhibits a heavy mixing with the no,n*2 configuration. The reported "n,3d" band at 8.88 eV is reassigned to the 0-0 band of the 3'A1 -%'Al transition, where the minimum of 3'Al results from an avoided crossing between n,n* and n,3p,. This explains the apparent large quantum defect and other anomalies reported for the so-called "n,3d" band.

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Section: + -mentioning

confidence: 96%

Section: Co Stretch Potential Curves For Valence and Rydberg Statmentioning

confidence: 99%

Spectroscopy of Formaldehyde. 1. Ab Initio Studies on Singlet Valence and Rydberg States of Planar H2CO, with Emphasis on 1(.pi.,.pi.) and 1(.sigma.,.pi.)

Hachey¹,

Bruna²,

Grein³

1995

J. Phys. Chem.

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“…Exceptions are the 0; band of n,3s, for which vibronic interaction with u, T * / T , T * may play a role, as outlined in [7]. The small calculated f-value for the 8.32 eV band may be due to the fact that both the D = 3 level of T, ,rr*/n2 and the D = 1 level of n, 3 p , lie close to the barrier in the 2lA, potential, which was not taken into account in the calculations.…”

Section: T T* State In Formaldehyde and Thioformaldehydementioning

confidence: 99%

The ?, ?* state in formaldehyde and thioformaldehyde

Grein

Hachey

1996

Int. J. Quantum Chem.

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mFor formaldehyde, the C -0 stretch potential of '(T, r*) crosses all 'A, Rydberg \r, r* + 2 system to these Rydberg states. For thioformaldehyde, the situation is similar but a shift in the potentials allows for direct observation of '(r, T * ) . In its ' ( T , T * ) state, H,CO is planar, having a low barrier of about 0.2 eV toward the nonplanar '(v, T * > state. For H,CS, the planar conformation of ' ( T , r*) is a saddle point, with '(v, r*) being the global minimum on the 2'A' surface. The triplet r, r* states of H,CO and H,CS are nonplanar, having inversion barriers of 0.1 and 0.05 eV, respectively. For both H,CO and H,CS, the T , r* configuration also crosses the ground-state configuration, which explains predissociation and radiationless transitions of some Rydberg states.otentials, such as n, 3p,, n, 3d,,, etc., thereby transferring the intensity of the unassigned 0 1996 John Wiley & Sons, Inc.

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“…According to Guyon et al [8], the p ,3p photoionization spectrum contains a short vibrational progression with a rather small spacing (< 300 cm -1 ), which was assumed to correspond to t 4 , since a similar feature had previously been reported for 1 1 B 2 (n ,3s ) of H 2 CO [30,31,43]. However, in a more detailed study of this H 2 CO band, Lessard and Moule [44] came to the conclusion that the complex vibrational structure involved excitations of the b 2 modes as well.…”

Section: Adiabatic Co Stretch Potential Curvesmentioning

confidence: 98%

“…For the R (CO) potential curves, the R (CH) distances and CH 2 angle were kept ® xed at the experimental values of H 2 CO, given in [30]. For the doublet states, up to four states (roots) were obtained from the secular CI equations.…”

Section: Technical Detailsmentioning

confidence: 99%

The electronic structure of the H2CO+ radical and higher Rydberg states of H2CO

Grein¹

1998

Molecular Physics

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Several properties of H 2 CO + (e.g., equilibrium geometries, harmonic vibrational frequencies and infrared intensities, ionization potentials, electronic transition energies, and R (CO) potential curves) have been calculated at the ab initio level (MP2 and MRDCI). The electronic states X 2 B 2 , 1 2 B 1 and 1 2 A 1 are found to be planar, contrary to recent speculations by experimentalists. A low vibrational frequency in the X 2 B 2 ionization spectrum, assumed in the literature to correspond to the out-of-plane motion of the cation, is reassigned to the asymmetric t 6 (CH 2 ) mode. The infrared absorption spectrum of the ground state is governed by the CH stretching modes, whereas t 2 (CO) is practically infrared inactive. The lowest quartet states 1 4 A Â Â and 1 4 A Â are non-planar. Vertical excitation energies for several members of the p ® Ryd series of H 2 CO converging to 1 2 B 1 of H 2 CO + are presented. From the approximate R (CO) potential curves for low-lying p ® Ryd and s ® Ryd states, the interactions between these H 2 CO states and X 2 B 2 and 1 2 B 1 of H 2 CO + are discussed in relation to observed autoionization processes.

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Configuration interaction studies on the S₂surface of H₂CO: 2¹A′(σ, π/π, π) as perturber of 1¹B₂(n, 3s)

Cited by 21 publications

References 37 publications

Spectroscopy of Formaldehyde. 1. Ab Initio Studies on Singlet Valence and Rydberg States of Planar H2CO, with Emphasis on 1(.pi.,.pi.) and 1(.sigma.,.pi.)

Spectroscopy of Formaldehyde. 1. Ab Initio Studies on Singlet Valence and Rydberg States of Planar H2CO, with Emphasis on 1(.pi.,.pi.) and 1(.sigma.,.pi.)

The ?, ?* state in formaldehyde and thioformaldehyde

The electronic structure of the H2CO+ radical and higher Rydberg states of H2CO

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