States Of Ketene Research Articles

Effective rotational constants for the three lowest vibrational states of ketene

This paper deals with the least-squares determination of effective rotational constants for the lowest three vibrational states of the ketene (CH2CO) molecule:v 5,v 6 andv 9. Several hundred rotational lines have been assigned in high-resolution Fourier-transform infrared spectra and were fitted to a standard, Watson Hamiltonian in theA-reduction formalism.

Examination of the ketene 1B 1 state photodissociation dynamics by far-ultraviolet resonance Raman spectroscopy

The 1B 1 state of ketene has been examined by resonance Raman spectroscopy with excitation between 217 and 200 nm. The fundamentals ( v 2, v 3, v 4), overtones (2 v 2, 3 v 2, 2 v 5, 2 v 6), and the combination bands of v 2, v 3, v 4, and 2 v 5 and 2 v 6 are found to be resonantly enhanced. The intensity of the out-of-plane bend vibrational overtones 2 v 5 and 2 v 6, and the absence of in-plane bend features in the Raman spectra indicate that the initial dynamics of the CH 2CO 1B 1 dissociation proceeds along a C I s pathway in which the CCO skeleton of ketene bends out of the CH 2 plane. The experimental result is compared with the ab initio predictions of the initial dissociation pathway.

Reaction paths for the dissociation ã 3A″ CH2CO→X̃ 3B1 CH2 + X̃ 1Σ+ CO

An ab initio investigation of the (CIIs) in-plane bent 3A″ CH2CO→X̃ 3B1 CH2+X̃ 1∑+CO and the (CIs) out-of-plane bent 3A′ CH2CO→X̃ 3B1 CH2+X̃ 1∑+CO dissociation paths has been performed. Geometrical structures, vibrational frequencies, and quadratic force constants have been determined at the DZP SCF and DZP CISD levels of theory for the X̃ 1A1, 3A″, and 3A′ states of ketene and for the 3A″ and 3A′ transition states for dissociation. The DZP CISD structure for à 1A″ ketene is also reported. Final energetic predictions for triplet ketene dissociation have been obtained from large-basis (QZ2P and QZ2P+f) UMP4(SDTQ) calculations at the DZP CISD geometries. The CIIs stationary point for 3A″ ketene dissociation is a true transition state with r(C–C)=2.071 Å at the DZP CISD level of theory. The corresponding CIs stationary point for 3A′ ketene is actually a super transition state for the interconversion of two equivalent 3A″CIIs transition states for dissociation. Final theoretical predictions of Te=19 400 cm−1 and T0=19 150 cm−1 are made for the adiabatic excitation energy of the ã 3A″ state of ketene, and a value of 22.3 kcal/mol is proposed for the 3A″ dissociation energy.

Ground and first excited states electrostatic molecular potentials of ketene and diazomethane

INDO wavefunctions for 1A 1, 1A″ and 3A″ states of ketene and diazomethane, obtained with a RHF technique, after some geometry optimization for the excited states, are used to obtain electrostatic molecular potentials under ZDO assumptions. Ground-state results agree with the experimental behaviour and also with other theoretical calculations for both molecules.

Photodecomposition of ketene to form methylene

Correlation curves for a least motion departure path of methylene in the photocomposition of ketene are interpreted in terms of least energy paths. It is concluded that the first excited triplet state of ketene can probably form 3CH2(3B2) and 1CH2(1 A 1) relatively rapidly and the first excited singlet state can give 3CH2(3 B 2) easily in a near least motion path. However, the formation of 1CH2(1 A 1) from the first excited singlet state of ketene by a near-least motion path appears to be highly improbable.

The Triplet State of Ketene

Ketene quenches the phosphorescence of both biacetyl and hexafluoroacetone. Although the quenching of hexafluoroacetone emission is nearly collision-controlled, that of biacetyl is much less efficient. The large difference in the rate constants is attributed to endothermic energy transfer from triplet biacetyl to ketene and exothermic energy transfer from triplet HFA to ketene. From the endothermicity, the lowest triplet state of ketene is estimated to be at 61 ± 1 kcal/mol above its ground state. No sensitized photodecomposition of ketene occurs as a result of energy transfer from either biacetyl or hexafluoroacetone.