Collisional deactivation of singlet methylene in the photolysis of ketene

1969 ◽  
Vol 47 (18) ◽  
pp. 3345-3353 ◽  
Author(s):  
R. A. Cox ◽  
K. F. Preston
Keyword(s):  
Carbon Monoxide ◽  
Quantum Yield ◽  
Ground State ◽  
Inert Gases ◽  
Inert Gas ◽  
Quantum Yields ◽  
Electronic Relaxation ◽  
Excited Singlet ◽  
State Formula ◽  
Singlet Methylene

An investigation has been made into the effect of inert gas additions on product quantum yields for the photolysis at 2800 and 2490 Å of mixtures of ketene and oxygen and for the photolysis at 2800 Å of mixtures of ketene and carbon monoxide. Concentration ratios of O2 (or CO) to CH2CO were chosen so that the reaction of CH2(3Σg−) with CH2CO could be ignored and C2H4 formation could be attributed entirely to the reaction[Formula: see text]Quenching of the C2H4 quantum yield by inert gases was interpreted in terms of collisional deactivation of CH2(1A1) to the ground state[Formula: see text]and rate constant ratios k2/k1 have been determined for a number of gases: He (0.018), Ar (0.014), Kr (0.033), Xe (0.074), N2 (0.052), N2O (0.10), CF4 (0.047), C2F6 (0.11), and SF6 (0.045). It has been assumed that collision-induced intersystem crossover in excited singlet ketene makes an insignificant contribution to the observed quenching effects, but it has not been possible to verify this assumption experimentally. The mechanism of collision-induced electronic relaxation of singlet methylene is discussed in the light of the results.

Photolysis of ketene. I

1968 ◽  
Vol 46 (14) ◽  
pp. 2353-2360 ◽  
Author(s):  
A. N. Strachan ◽  
D. E. Thornton
Keyword(s):  
Carbon Monoxide ◽  
Quantum Yield ◽  
Triplet State ◽  
Singlet State ◽  
Inert Gases ◽  
Inert Gas ◽  
Excited Singlet State ◽  
Intersystem Crossing ◽  
Excited Singlet ◽  
Increasing Temperature

Ketene has been photolyzed at 3660 and 3130 Å both alone and in the presence of the inert gases C4F8 and SF6. The quantum yield of carbon monoxide has been determined at both wavelengths as a function of pressure and temperature. At 3660 Å the quantum yield decreases with increasing pressure but increases with increasing temperature. At 3130 Å the quantum yield with ketene alone remains 2.0 at both 37 and 100 °C at pressures up to 250 mm. At higher pressures of ketene or with added inert gas the quantum yield decreases with increasing pressure. The results are interpreted in terms of a mechanism in which intersystem crossing from the excited singlet state to the triplet state occurs at both wavelengths, and collisional deactivation of the excited singlet state by ketene is single stage at 3660 Å but multistage at 3130 Å.

THE REACTION OF ISOPROPANOL VAPOR WITH Hg 6 (3P1) ATOMS: PART I. PURE SUBSTRATE

1962 ◽  
Vol 40 (6) ◽  
pp. 1134-1139 ◽  
Author(s):  
Arthur R. Knight ◽  
Harry E. Gunning
Keyword(s):  
Quantum Yield ◽  
Hydrogen Production ◽  
Exposure Time ◽  
Resonance Line ◽  
Light Period ◽  
Inert Gas ◽  
Quantum Yields ◽  
Volatile Product ◽  
Intermittent Illumination ◽  
Static Conditions

The reaction of isopropanol vapor with Hg 6(3P1) atoms has been investigated under static conditions at 25 °C under continuous and intermittent illumination. The effect of added inert gas and isolation of the 2537 Å Hg resonance line were also studied.The products of the reaction are H2 (0.72), CH3COCH3 (0.25), CO, CH4, C2H6, CH3CHO, and H2O, with the numbers in parentheses representing the quantum yields at zero exposure time. The non-volatile product remaining in the cell was a mixture of C6-glycols, containing 98.6% pinacol, 1.2% 2-methyl-2,4-pentanediol, and ca. 0.2% or less of 2,5-hexanediol.Under intermittent illumination, the quantum yield of hydrogen production, measured as a function of light period, tL, rose linearly with log tL, and had a constant value of unity for tL < 0.45 msec. A mechanism is proposed involving the primary formation with perfect efficiency of isopropoxy radicals and H atoms.

Photochemistry of acetylene

1983 ◽  
Vol 61 (5) ◽  
pp. 850-855 ◽  
Author(s):  
H. Okabe
Keyword(s):  
Quantum Yield ◽  
Ground State ◽  
Vacuum Ultraviolet ◽  
Inert Gases ◽  
Primary Process ◽  
Fluorescence Studies ◽  
Ethynyl Radical ◽  
Absorption Of Light ◽  
Electronically Excited

Photochemical and fluorescence studies of acetylene initiated by absorption of light in the vacuum ultraviolet have been described. The photochemical primary process consists of (1) the formation of C2 + H2, (2) the production of C2H + H, and (3) the formation of a metastable acetylene. The quantum yield of process (1) is about 0.1 and that of process (2) is 0.06 at 1849 Å and 0.3 at 1470 Å. The metastable acetylene either reacts with ground state acetylene to produce diacetylene or is deactivated by collisions with the walls, inert gases, or by fluorescence. A quasicontinuous emission is observed in the 4000 to 6000 Å region when acetylene is exposed to incident wavelengths below 1305 Å. This emission is ascribed to an electronically excited ethynyl radical. The rates of reaction C2H + H2 → C2H2 + H and C2H + RH → C2H2 + R (RH = CH4, C2H6, C3H8) have been measured. The photochemistry of acetylene in the Jovian and Titan atmospheres is briefly discussed.

Activation energy barrier for intersystem crossing in platinum phthalocyanine

1976 ◽  
Vol 54 (6) ◽  
pp. 633-637 ◽  
Author(s):  
Tzer-Hsiang Huang ◽  
Klaus E. Rieckhoff ◽  
Eva-Maria Voigt
Keyword(s):  
Triplet State ◽  
Ground State ◽  
Energy Barrier ◽  
Singlet State ◽  
Quantum Yields ◽  
Intersystem Crossing ◽  
Singlet Ground State ◽  
Activation Energy Barrier ◽  
Excited Singlet ◽  
Platinum Phthalocyanine

Phosphorescence quantum yields and lifetimes of platinum phthalocyanine in α-chloronaphthalene solution are reported for temperatures from 1.3 K to 300 K. Activation energies of intersystem crossing are deduced and found to be Ea = 17 ± 3 cm−1 for crossing from the first excited singlet state to the lowest lying triplet state and Eap = 8 ± 1 cm−1 for crossing from the lowest lying triplet state to the singlet ground state.

Processus primaire de la photolyse et de la photo-oxydation de l'o-phényl-phénol

1980 ◽  
Vol 58 (21) ◽  
pp. 2230-2235 ◽  
Author(s):  
Louise-Marie Coulangeon ◽  
Gilles Perbet ◽  
Pierre Boule ◽  
Jacques Lemaire
Keyword(s):  
Quantum Yield ◽  
Singlet State ◽  
Excited Singlet State ◽  
Quantum Yields ◽  
Oxygen Effect ◽  
Dual Fluorescence ◽  
Excited Singlet ◽  
Photochemical Process ◽  
Phenoxy Radicals ◽  
Effect Of Oxygen

The dual fluorescence observed in aqueous solution of o-phenyl-phenol is attributed to a deprotonation equilibrium in the excited singlet state. The effect of oxygen on the primary photochemical process of formation of phenoxy radicals can be explained in a parallel study of the variations of fluorescence and photo-oxidation quantum yields of this phenolic compound at different pH. It is shown that photoionisation occurs only from the excited singlet state of the phenolate form. Oxygen inhibits recombination of the solvated electron and phenoxy radical. Increase of quantum yield for the disappearance of irradiated o-phenyl-phenol in degased solution also is observed in the presence of electron scavengers like Cd2+ or NO3− ions. Even when the phenoxy radicals are not able to react with oxygen, quantum yield for the disappearance of the phenolic compounds is higher in an aerated than in a degassed solution; the oxygen effect on the primary photochemical step may explain this difference.

Reaction of Oxygen Atoms, O(3P), with Ethylene in Liquid Nitrogen Solution

1973 ◽  
Vol 51 (3) ◽  
pp. 373-381 ◽  
Author(s):  
Shun-Ichi Hirokami ◽  
R. J. Cvetanović
Keyword(s):  
Quantum Yield ◽  
Ethylene Oxide ◽  
Molecular Oxygen ◽  
Liquid Nitrogen ◽  
Rate Constant ◽  
Ground State ◽  
Relative Rate ◽  
Quantum Yields ◽  
Relative Rate Constant ◽  
Oxygen Atoms

The reaction of ground-state oxygen atoms, O(3P), with ethylene and ethylene-d4 in liquid nitrogen solution at 77° K has been studied. The major and perhaps the exclusive products are ethylene oxide and acetaldehyde. The ratio of acetaldehyde to ethylene oxide is 1.2 ± 0.1 for ethylene and 0.91 ± 0.09 for ethylene-d4. Much smaller amounts of formaldehyde and trace quantities of cyclopropane are also observed.The effect of the concentration of ethylene on the quantum yields of addition products was measured. A limiting quantum yield of oxygen atoms scavenged by ethylene to form the addition products was 0.12 + 0.01. The low quantum yield suggests an appreciable cage recombination of the ground-state oxygen atoms with the trace amounts of molecular oxygen present. The effect of the concentration of added oxygen on the product yields and the relative rate constant for the addition of O(3P) to molecular oxygen and to ethylene were determined. The ratio [Formula: see text] is 6.0 ± 1.0 and the relative rate constant for the addition of O(3P) to ethylene and to ethylene-d4, [Formula: see text], is 2.0 ± 0.1.The type of products formed and the isotope effects observed are discussed in terms of the mechanism of addition of O(3P) atoms to ethylene.

Der Substituenteneinfluß auf die Fluoreszenz des 1.3-Diphenyl-2-pyrazolins / Substituent Effects on the Fluorescence of 1,3-Diphenyl-2-pyrazoline

1976 ◽  
Vol 31 (9) ◽  
pp. 1248-1255 ◽  
Author(s):  
H. Strähle ◽  
W. Seitz ◽  
H. Güsten
Keyword(s):  
Absorption Spectra ◽  
Ground State ◽  
Phenyl Ring ◽  
Fluorescence Spectra ◽  
Singlet State ◽  
Fluorescence Decay ◽  
Quantum Yields ◽  
Excited Singlet ◽  
Fluorescence Quantum Yields ◽  
Absolute Fluorescence

The electronic absorption spectra, absolute fluorescence spectra and fluorescence quantum yields as well as the fluorescence decay times of nine 1,3-diphenyl-2-pyrazolines substituted in the para-position of the 1-phenyl ring and of 19 substituted in the paraposition of the 3-phenyl ring were measured in degassed benzene at room temperature. The fluorescence quantum yields are about 0.90 with the exception of the NO2- and J-substituted 1,3-diphenyl-2-pyrazolines. The fluorescence decay time ranges from 2 to 4 nsec. The natural fluorescence lifetimes determined experimentally agree well with those calculated from the absorption spectra according to STRICKLER and BERG. A plot of the Hammett σp-values versus the energies of the absolute fluorescence maxima of the psubstituted 1- and 3-phenyl ring of the 2-pyrazoline system shows a statistically significant linear correlation with moderate precision. The linearity between ground state substituent constants and fluorescence energies reveals that the relative importance of the inductive and the resonance effects of the substituents remains constant during the transition from the ground state to the relaxed excited singlet state. In the excited singlet state of 1,3-diphenyl-2-pyrazoline the p-substituents provide more room for a larger charge displacement in the intramolecular charge-transfer. The structural bands in the fluorescence spectra resulting from strong electron accepting substituents in the para-position of the 1-phenyl ring are considered as the result of the ring breathing vibration due to a local excitation of the 1-phenyl ring.

Quantum yields of triplet formation in solutions of chlorophyll

1967 ◽  
Vol 296 (1447) ◽  
pp. 435-441 ◽  
Keyword(s):  
Direct Measurement ◽  
Ground State ◽  
Flash Photolysis ◽  
Quantum Yields ◽  
Intersystem Crossing ◽  
Excited Singlet ◽  
Ether Solution ◽  
Triplet Formation

The method of flash photolysis has been used for direct measurement of the quantum yields of triplet formation in dilute chlorophyll solutions at 23 °C. In ether solution, the triplet yields were found to be 0⋅64 and 0⋅88 for chlorophyll a and b , respectively. In very dry hydro­carbon solution, the yields decrease by at least a factor of 5. It is suggested that the low yields of fluorescence and intersystem crossing in dry solvents are due to dissociation of excited singlet dimer chlorophyll into ground state monomer species.

The primary process in the photolysis of hexafluoroacetone vapour II. The fluorescence and phosphorescence

1968 ◽  
Vol 306 (1487) ◽  
pp. 511-528 ◽  
Keyword(s):  
Quantum Yield ◽  
Singlet State ◽  
Quantum Yields ◽  
Reasonable Assumption ◽  
Excited Singlet ◽  
Vibrationally Excited ◽  
Absolute Value ◽  
Relative Quantum ◽  
Wide Range ◽  
Spectral Area

The relative quantum yields for the total and for the fluorescent emissions were studied over a wide range of ketone pressures with excitation at 254, 265, 313 and 366 nm. A spectral area technique showed that the absolute value of the ratio of the quantum yield for phosphorescence to that for fluorescence was zero at zero ketone pressure, but increased to ca . 6⋅1 at infinite ketone pressure; the limiting high-pressure value did not depend on whether excitation was at 265 or 313 nm. Quinine sulphate actinometry was used to determine an absolute value of φ ƒ ∞ = 0⋅0185 for λ excit. = 265 or 313 nm; thus φ p ∞ was 0⋅11 3 . With λ excit. = 254 nm a reasonable assumption was required to reach the same values. The quantum yield for the phosphorescence of biacetyl vapour was re-determined as 0⋅16 g by the same technique. φ ƒ did not extrapolate to zero at zero ketone pressure; hence emission must also occur from vibrationally excited molecules in the singlet nπ * state. The detailed shapes of the plots of φ ƒ and φ p against pressure are reported here but are discussed in part V, where the question of the mechanism of the vibrational relaxation in the excited singlet state is considered. Because the quantum yields obtained with excitation at 366 nm were independent of pressure, these data are qualitatively different from those obtained at shorter wavelengths and are discussed in the present paper.

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