The investigation of double-minimum potentials in molecules

The &([a-z]+);(3A2) and [Formula: see text] states of jet-cooled thiophosgene (Cl2CS) have been studied by optical–optical double resonance (OODR) spectroscopy. Two OODR schemes have been used to probe the [Formula: see text] state. One scheme uses selected vibronic levels of the &([a-z]+);(1A2) state as the intermediate state, while the other uses the vibrationless and 2131 levels of the &([a-z]+);(3A2) state. All of the vibronic levels in the 33 980−35 600 cm−1 region can be rationalized with the following origin band and fundamentals: 0° = 34 277 cm−1, v1 = 505 cm−1, v2 = 470 cm−1, v3 = 213 cm−1, v6 = 249 cm−1, 42 = 341 cm−1, 44 = 627 cm−1. The discrepancies among the various studies of the [Formula: see text] state will be discussed and reconciled. It is conjectured that the [Formula: see text] state potential along the C—S coordinate exhibits an asymmetric double-minimum potential resulting from the interaction of the 1A1 states arising from the [Formula: see text] configurations. The minimum corresponding to the [Formula: see text] configuration lies higher in energy and the principal decay mechanism for molecules pumped to its first few vibronic levels is fluorescence. On the other hand, molecules pumped to the minimum corresponding to the nominal [Formula: see text] configuration decay nonradiatively. The barrier height to inversion and the out-of-plane bending angle along the out-of-plane bending coordinate, v4, have been determined to be 945 cm−1 and 25°, respectively, by fitting quartic-quadratic and quadratic-Gaussian double-minimum potentials to the observed energy levels. The &([a-z]+);(3A2) state has been studied by a novel OODR scheme which uses the fluorescent vibrationless level of the [Formula: see text] state to monitor [Formula: see text]transitions. A vibronic analysis has been carried out and the following origin band and fundamentals derived for the &([a-z]+);(3A2) state: 0° = 17 499 cm−1, v1 = 923 cm−1, v2 = 474 cm−1, v3 = 247 cm−1, 42 = 297 cm−1, 44 = 560 cm−1, 46 = 741 cm−1. With the exception of a few corrections and additions, the results confirm the findings of previous studies, notably regarding the bent geometry and barrier height to inversion. An overall comparison of the data suggests that the wavenumber of v6 in theÃ(1A2) state is 279 cm−1 instead of 189 cm−1.

Section: Fig 7 Jet-cooled ~( ' A~ O~) -Z~(~a~~' ) -~( ' A~ O~)mentioning

confidence: 99%

Optical–optical double resonance study of the and &([a-z]+);(³A₂) states of thiophosgene

Simard¹,

Mackenzie²,

Hackett³

et al. 1994

“…We also investigated the possibility of assigning the 7 cm-' frequency to the inversion splitting 14'-(0'-) -0". From the TI inversion potentials for CH,CHO and CD,CDO and the assignment of the 503 cm-' frequency in the CH,CHO spectrum to the 14'' level (Table 2), we calculate an inversion splitting of 41-45 cm-I for CH,CHO by the method of Coon et al (10). As such intervals are not observed in the CH,CHO spectrum, this hypothesis has been rejected.…”

mentioning

confidence: 99%

The electronic spectra of acetaldehyde-h₄ and -d₄

Yakovlev¹,

Godunov²

1992

N. N. YAKOVLEV and I. A. GODUNOV. Can. J. Chem. 70, 931 (1992).The r 7 3~" t X'A' electronic absorption spectra of acetaldehyde-h4 and -d4 were recorded in the vapour phase at room temperature. The major experimental requirement was a high pressure X path length (650 Torr X 140 m). The vibrational structure of these electronic transitions was interpreted in terms of the torsional modes vj5 and vy5 attached to the vi4 out-of-plane bending mode. The main CH3CH0 results agreed with those obtained earlier (Moule and Ng); the values of the 0: transition and torsional barrier height were 27240.1 and 590 cm-' respectively. Three inversion (out-ofplane bending) energy levels in the excited ti3A" state were found and the inversion potential function was determined with a barrier height of 11 10 cm-I. The CD3CD0 spectrum confirmed the CH,CHO analysis. The values of the 0: transition and torsional barrier height were equal to 27270 and 610 cm-I.

“…7. The calculations were performed by modelling the excited state double minimum potential-energy along the inversion vibration coordinate by a harmonic function perturbed by a Gaussian barrier, following the method of Coon et al (18). This model has previously been used successfully to calculate the inversion vibrational energies and the equilibrium out-of-plane angles of the lowest triplet and excited singlet states of a number of tetraatomic carbonyls (19) and thiocarbonyls (3,20).…”

Section: Resultsmentioning

confidence: 99%

“…This model has previously been used successfully to calculate the inversion vibrational energies and the equilibrium out-of-plane angles of the lowest triplet and excited singlet states of a number of tetraatomic carbonyls (19) and thiocarbonyls (3,20). The function has the form where Qmin is the mass weighted coordinate at On,,,, r is the C-S bond distance, and p. is the reduced mass (18). The equilibrium geometry of Br2CS in its A (or any other excited) state has not been determined so that p. and r are not known.…”

Section: Resultsmentioning

confidence: 99%

Vibronic analysis of the spectrum of Br₂CS

Simard¹,

Steer²

1985

[Formula: see text] fluorescence excitation and emission spectra of Br2CS have been recorded. A vibronic analysis shows that the molecule is non-planar in the [Formula: see text] state with an equilibrium out-of-plane angle of 13° and a barrier to inversion of l64 cm−1. Upper state vibrational frequencies of modes 1, 2, 3, 4, and 6 have been obtained. Comparisons with other tetraatomic thiocarbonyls support the assignments. A ground state C—Br dissociation energy of 52.3 kcal mol−1 has been obtained from the onset of diffuseness in the [Formula: see text] spectra. A search for phosphorescence proved unsuccessful.