The photolysis and thermal decomposition of pyruvic acid in the gas phase

1985 ◽  
Vol 63 (2) ◽  
pp. 549-554 ◽  
Author(s):  
S. Yamamoto ◽  
R. A. Back
Keyword(s):  
Thermal Decomposition ◽  
Gas Phase ◽  
Pyruvic Acid ◽  
Light Emission ◽  
Singlet State ◽  
Hydrogen Atom Transfer ◽  
Triplet States ◽  
Primary Process ◽  
Weak Absorption ◽  
Singlet And Triplet States

The photolysis of pyruvic acid vapour has been studied at wavelengths of 366, 345, and 320 nm, at a temperature of 340 K and pressures from about 1 to 10 Torr. Products observed were CO2 and CH3CHO, with the former always in excess, and a quantum yield of CO2 of 0.9 ± 0.1 at 366 nm. Light emission was also observed, and from the effect of added O2 it was concluded that emission occurred from both singlet and triplet states. It is suggested that the primary process in the photolysis is an internal hydrogen-atom transfer followed by dissociation into CO2 and CH3—C—OH, with the latter then rearranging to give CH3CHO and other products.The absorption spectrum is reported; the first system begins at about 380 nm, rising to a maximum at about 350 nm, with εmax = 10 M−1 cm−1, and is attributed to the first excited π* ← n+ singlet state. Weak absorption below 300 nm is probably due to the π* ← n− state and much stronger absorption below 220 nm to the π* ← π state.The thermal decomposition was studied briefly at temperatures from 455 to 584 K and pressures from about 0.8 to 7 Torr. Products were the same as in the photolysis, and Arrhenius parameters of log A (s−1) = 7.19 and E = 27.7 kcal/mol were obtained, based on the formation of CO2, which was apparently a simple, homogeneous unimolecular process.

Emission and Deactivation of the Excited States of 2,3-Pentanedione

1972 ◽  
Vol 50 (9) ◽  
pp. 1338-1344 ◽  
Author(s):  
A. W. Jackson ◽  
A. J. Yarwood
Keyword(s):  
Triplet State ◽  
Gas Phase ◽  
Excited States ◽  
Singlet State ◽  
Triplet States ◽  
Excited Singlet ◽  
Vibrationally Excited ◽  
Singlet Level ◽  
Singlet And Triplet States ◽  
Fluorescence And Phosphorescence

Vibrationally excited singlet and triplet states of 2,3-pentanedione are formed by photolysis at 365 nm. The processes removing these excited states in the gas phase are studied by measuring the fluorescence and phosphorescence yields. Fluorescence can occur from the vibrationally excited, as well as the vibrationally equilibrated, singlet state. The fluorescence and phosphorescence data are considered in terms of mechanisms which involve either weak or strong collisions. Although the data cannot distinguish between the alternatives, there are two significant conclusions. The fluorescence data require that emission occur from at least two levels in the singlet manifold. To explain the phosphorescence data, the highest emitting singlet level must not lead to a vibrationally equilibrated triplet state.

The gas-phase photochemistry and thermal decomposition of glyoxylic acid

1985 ◽  
Vol 63 (2) ◽  
pp. 542-548 ◽  
Author(s):  
R. A. Back ◽  
S. Yamamoto
Keyword(s):  
Thermal Decomposition ◽  
Carbon Monoxide ◽  
Absorption Spectrum ◽  
Gas Phase ◽  
Singlet State ◽  
Glyoxylic Acid ◽  
Static System ◽  
First Order ◽  
Increasing Temperature ◽  
Homogeneous Formation

The photolysis of glyoxylic acid vapour has been studied at five wavelengths, 382, 366, 346, 275, and 239 nm, and pressures from about 1 to 6 Torr, at a temperature of 355 K. Major products were CO2 and CH2O, initially formed in almost equal amounts, while minor products were CO and H2. Except at 382 nm, the system was complicated by the rapid secondary photolysis of CH2O. Three primary processes are suggested, each involving internal H-atom transfer followed by dissociation.The absorption spectrum is reported and shows the three distinct absorption systems. A finely-structured spectrum from about 320 to 400 nm is attributed to a transition to the first excited π* ← n+ singlet state; a more diffuse absorption ranging from about 290 nm to a maximum at 239 nm is assigned to the π* ← n− state, while a much stronger absorption beginning below 230 nm is attributed to the π* ← π transition. Product ratios vary with wavelength and depend on which excited state is involved.The thermal decomposition was studied briefly in a static system at temperatures from 470 to 710 K and pressures from 0.4 to 8 Torr. Major products were again CO2 and CH2O, but the latter was always less than stoichiometric. First-order rate constants for the apparently homogeneous formation of CO2 are described by Arrhenius parameters log A (s−1) = 7.80 and E = 30.8 kcal/mol. Carbon monoxide and H2 were minor products, and the CO/CO2 ratio increased with increasing temperature and showed some surface enhancement at lower temperatures. The SF6-sensitized thermal decomposition of glyoxylic acid, induced by a pulsed CO2 laser, was briefly studied, with temperatures estimated to be in the 1100–1600 K range, and the CO/CO2 ratio increased with increasing temperature, continuing the trend observed in the static system.

Molecular orbital studies of the singlet and triplet states of formylmethylene conformers

1991 ◽  
Vol 69 (11) ◽  
pp. 1630-1635 ◽  
Author(s):  
Ratnakar K. Gosavi ◽  
Manuel Torres ◽  
Otto P. Strausz
Keyword(s):  
Singlet State ◽  
Closed Shell ◽  
Basis Set ◽  
Planar Geometry ◽  
Present Calculation ◽  
Triplet States ◽  
Excited Singlet ◽  
Singlet And Triplet States ◽  
Ci Calculations ◽  
Single Configuration

The energies and geometries of the low-lying electronic states of formylmethylene have been calculated at the SCF and CI levels using 6-31G** basis set. In agreement with previous reports and accumulated experimental observations, the ground state is the carbenoid triplet with a planar geometry. Also, in agreement with all previous single configuration SCF and CI calculations, the lowest excited singlet state is computed to be the nonplanar closed shell carbenoid structure. In contrast, accumulated experimental evidence along with previously reported MC–SCF results require this state to be planar. The present calculation predicts the existence of a (σ–σ) 1,3-diradical 1A′ state, which appears to be identical to the MC–SCF lowest singlet state, but this state lies some 11 kcal/mol above the closed shell carbenoid 1A state. Apparently, single configuration SCF methods are inadequate for the correct description of the electronic manifold of formylmethylene. Key words: formylmethylene, singlet and triplet states, ab initio MO calculations, conformers, molecular structure.

The mechanism of the gas phase photolysis of acetone

1966 ◽  
Vol 290 (1423) ◽  
pp. 563-582 ◽  
Keyword(s):  
Gas Phase ◽  
Order Rate Constant ◽  
Electronic Energy ◽  
Intersystem Crossing ◽  
Triplet States ◽  
Excited Singlet ◽  
First Order ◽  
Electronic Energy Transfer ◽  
Vibrational Levels ◽  
Singlet And Triplet States

A mechanism for the photolysis of acetone has been derived from experimental data including studies on the photosensitized isomerization of olefines. Dissociation into methyl and acetyl radicals occurs from both the first excited singlet and triplet states; the rate constants for excitation by light of 3130 Å wavelength are 2.5 x 10 16 exp ( —16900/ RT ) and 2.5 x 10 10 exp ( — 6400/ RT ) 1. mole -1 s -1 respectively. At low intensities of absorption, decomposition of acetyl radicals predominates over radical-radical interactions. The triplet state is extensively populated at moderate temperatures, the yield at 48 °C being 0.98. The low phosphorescence efficiency of acetone can be ascribed to intersystem crossing to the ground state for which the first order rate constant is 1.25 x 10 5 s -1 . The isomerization data requires the recognition of at least two vibrational levels of the acetone triplet, the rate of electronic energy transfer depending upon the excess energy possessed by the donor

Lifetime studies of the biacetyl excited singlet and triplet states in the gas phase at 25.deg.

1972 ◽  
Vol 94 (1) ◽  
pp. 13-19 ◽  
Author(s):  
Howard W. Sidebottom ◽  
Charles C. Badcock ◽  
Jack G. Calvert ◽  
Blaine R. Rabe ◽  
Edward K. Damon
Keyword(s):  
Gas Phase ◽  
Triplet States ◽  
Excited Singlet ◽  
Singlet And Triplet States ◽  
Lifetime Studies

Low-lying activated states of chloroiridium phthalocyanine aggregates in glassy solution at low temperatures

1988 ◽  
Vol 66 (1) ◽  
pp. 86-92 ◽  
Author(s):  
W.-H. Chen ◽  
K. E. Rieckhoff ◽  
E.-M. Voigt
Keyword(s):  
Singlet State ◽  
Torsional Oscillation ◽  
Zero Point ◽  
Triplet States ◽  
Excited Singlet ◽  
Glassy Solution ◽  
Ground Singlet State ◽  
Modes Of Vibration ◽  
State Formula ◽  
Singlet And Triplet States

Studies of phosphorescence intensities and lifetimes of two chloroiridium phthalocyanine aggregates in α-chloronaphthalene between 5 and 80 K have revealed the existence of low-lying activated states only a few tens of cm−1 above the zero-point vibration in both lowest singlet and triplet states. From the data, activation energies of intersystem crossings between the two multiplicities associated with these states have been obtained as follows: for crossing from the first excited singlet to the lowest triplet state, Ea = 42 ± 10 and 29 ± 10 cm−1, respectively, for the two aggregates; for crossing from the lowest triplet to the ground singlet state, [Formula: see text] and 23 ± 5 cm−1, respectively. These activated states are tentatively attributed to certain intermolecular modes of vibration in aggregates. Specifically, they fit the model of molecular torsional oscillation of two and three parallel-sheet arrangements. On the basis of these findings, we propose that the first Ea (or [Formula: see text]) is the fundamental librational frequency of the dimer and the second Ea (or [Formula: see text]) is that for the trimer.

Photocyclization of 2-vinylbiphenyls: stereochemistry of the triplet state cyclization

1985 ◽  
Vol 63 (8) ◽  
pp. 2192-2196 ◽  
Author(s):  
René Lapouyade ◽  
Claude Manigand ◽  
Aziz Nourmamode
Keyword(s):  
Excited State ◽  
Triplet State ◽  
Trans Isomer ◽  
Singlet State ◽  
Membered Ring ◽  
Quantum Yields ◽  
Triplet States ◽  
Singlet Excited State ◽  
Singlet And Triplet States ◽  
Cis Isomer

The photochemistry of five- to eight-membered ring containing 2-cycloalkenyl biphenyls was examined under direct and sensitized irradiation. From the singlet excited state only trans 9,10-cycloalkyl-9,10-dihydrophenanthrenes were obtained. From the triplet state the trans isomer was exclusively formed from 2-cyclopentenyl and 2-cyclohexenyl biphenyls while the cis isomer also appeared with 2-cycloheptenyl and 2-cyclooctenyl biphenyls. We propose that the cis isomers resulted from the cyclization of the perpendicular triplet of cycloheptenyl biphenyl and from the perpendicular and trans triplet of cyclooctenyl biphenyl. Whereas the photocyclization of 2-vinylbiphenyls was regarded as a singlet-state reaction, the quantum yields of reaction of 2-cycloalkenyl biphenyls, from both singlet and triplet states, were high (ΦS = 0.20–0.26; ΦT = 0.15–0.46).

Formation of a Bound State in the Presence of Repulsive Interaction

2003 ◽  
Vol 17 (18n20) ◽  
pp. 3242-3250 ◽  
Author(s):  
J. D. Fan ◽  
Y. M. Malozovsky
Keyword(s):  
Triplet State ◽  
Multiple Scattering ◽  
Singlet State ◽  
Effective Interaction ◽  
Bound State ◽  
Repulsive Interaction ◽  
Triplet States ◽  
Hartree Potential ◽  
Singlet And Triplet States ◽  
T Matrix

We have examined the effective interaction of two fermions in terms of the T-matrix and shown that there are two different series of ladder diagrams in describing the effective interaction: (1) the exchange ladder diagrams giving rise to the T-matrix for the triplet state with poles for attractive interaction and (2) the Hartree ladder diagrams describing the multiple scattering on the Hartree potential and producing the T-matrix for the singlet state with poles for repulsive interaction. It is verified that a bound state of two fermions in the singlet state exists only in the presence of repulsive interaction between them. We further argue that the potential in the Schrodinger equation should be spin-dependent to describe both the singlet and triplet states.

The Thermal Decomposition of Tertiary Butyl Chloride in the Presence of Sulphur Hexafluoride

1962 ◽  
Vol 15 (3) ◽  
pp. 437 ◽  
Author(s):  
RL Failes ◽  
VR Stimson
Keyword(s):  
Thermal Decomposition ◽  
Gas Phase ◽  
Simple Theory ◽  
Triplet States ◽  
Phase Decomposition ◽  
Butyl Chloride ◽  
Sulphur Hexafluoride ◽  
Tertiary Butyl

No acceleration of the gas-phase decomposition of tertiary butyl chloride at 284-309 �C occurs in the presence of sulphur hexafluoride. This behaviour contrasts with that of a variety of unimolecular decompositions probably occurring via triplet states where an extension of the simple theory of activation has been found necessary.

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