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.

The photolysis of hexafluoroacetone

1956 ◽  
Vol 234 (1199) ◽  
pp. 476-488 ◽  
Keyword(s):  
Quantum Yield ◽  
Initial Step ◽  
Excited Molecule ◽  
Inert Gases ◽  
Wide Range ◽  
Electronically Excited ◽  
Photolytic Decomposition ◽  
Long Lifetime ◽  
The Stability ◽  
Excellent Source

The photolytic decomposition of hexafluoroacetone has been studied over a wide range of temperatures and pressures using light of wavelength 3130 Å. The initial step involves the production of CF 3 radicals, and the only products are C 2 F 6 and CO. The reaction is an excellent source of CF 3 radicals. The quantum yield diminishes with increasing pressure. A mechanism is suggested involving the participation of an electronically excited molecule of comparatively long lifetime, and the effect of various inert gases on the stability of this species is discussed.

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.

THE Hg 6(3P1)-PHOTOSENSITIZED DECOMPOSITION OF NITRIC OXIDE

1961 ◽  
Vol 39 (12) ◽  
pp. 2549-2555 ◽  
Author(s):  
Otto P. Strausz ◽  
Harry E. Gunning
Keyword(s):  
Nitric Oxide ◽  
Quantum Yield ◽  
Ground State ◽  
Pressure Range ◽  
Oxides Of Nitrogen ◽  
Total Rate ◽  
A Value ◽  
Electronically Excited ◽  
Static Conditions ◽  
Observed Behavior

The reaction of NO with Hg 6(3P1) atoms has been studied under static conditions at 30°, over the pressure range 1–286 mm. The products were found to be N2, N2O, and higher oxides of nitrogen. At NO pressures exceeding 4 mm, the total rate of formation of N2+N2O was constant, while the ratio N2O/N2 increased linearly with the substrate pressure. The rate was found to vary directly with the first power of the intensity at 2537 Å, and a value of 1.9 × 10−3 moles/einstein was established for the quantum yield of N2 + N2O production. In the proposed mechanism, reaction is attributed to the decomposition of an energy-rich dimer, (NO)2*, which is formed by the collision of electronically excited (4II) NO molecules with those in the ground state. The (NO)2* species is assumed to decompose by the steps: (NO)2* → N2 + O2 and (NO)2* + NO → N2O + NO2. The mechanism satisfactorily explains the observed behavior of the system.

The Vacuum Ultraviolet Photolysis of Cyclopentanone

1972 ◽  
Vol 50 (24) ◽  
pp. 3938-3943 ◽  
Author(s):  
Alfred A. Scala ◽  
Daniel G. Ballan
Keyword(s):  
Quantum Yield ◽  
Carbonyl Group ◽  
Incident Energy ◽  
Vacuum Ultraviolet ◽  
Quantum Yields ◽  
Electronically Excited ◽  
Ultraviolet Photolysis

In the vacuum ultraviolet photolysis of cyclopentanone, the major modes of fragmentation of the electronically excited ketone are:[Formula: see text]The sum of the quantum yields for reactions A and B is 0.87 at 147.0 nm and these reactions become less important as the incident energy is increased. A pressure study at 147.0 nm of the partitioning of the tetramethylene diradical between paths A and B indicates that the ratio kA/kB is approximately 8. The quantum yield for reaction 8 is only 0.02. The remainder of the decomposition of cyclopentanone is accounted for by reactions 4 and 5, which appear to become more significant as the incident energy increases. The mechanisms for reactions 6 and 8 are best interpreted in terms of diradicals of structure (CH2)n where n = 1, 3, and 4. The lack of non-acyl σ-cleavage at 147.0 nm is an indication that the absorption of energy occurs at the carbonyl group.

The kinetics of elementary reactions involving the oxides of sulphur III. The chemiluminescent reaction between sulphur monoxide and ozone

1966 ◽  
Vol 295 (1443) ◽  
pp. 380-398 ◽  
Keyword(s):  
Ground State ◽  
Vibrational Energy ◽  
Excited Electronic State ◽  
Fluorescence Yield ◽  
Collisional Quenching ◽  
Kcal Mole ◽  
Elementary Reactions ◽  
Fluorescence Studies ◽  
Chemiluminescent Reaction ◽  
Electronically Excited

The chemiluminescent reaction between sulphur monoxide (SO) and ozone has been studied in a fast flow system at pressures between 0·3 and 3·0 mmHg, These species undergo a rapid bimolecular reation (1) SO + O 3 = SO 2 + O 2 + 106 kcal/mole (1) to yield ground state products, where k 1 = 1·5 x 10 12 exp ( –2100/ RT ) cm 3 mole -1 s -1 . This reaction also yields electronically excited SO 2 molecules in the 1 B and 3 B 1 states. The 1 B SO 2 molecules are produced with up to 16 kcal/mole vibrational energy. Emission from the longer lived 3 B 1 state is vibrationally relaxed and provides no information about the initial energy distribution. Comparison with fluorescence studies shows that the 3 B 1 SO 2 molecules are produced mainly by collisional quenching of SO 2 molecules formed in the 1 B state. The formation of electronically excited SO 2 is also a simple bimolecular process, but it involves a higher energy barrier than formation of ground state SO 2 . Our measurements on the chemiluminescence, when combined with data on the quenching of the SO 2 fluorescence, yield the rate constants k 1a = 10 11 exp ( – 4200/ RT ) and k lb ≯ 3 x 10 10 exp ( –3900/ RT ) cm 3 mole -1 s -1 for the bimolecular reactions SO + O 3 = SO 2 ( 1 B ) + O 2 + 21 kcal/mole, (1 a ) SO + O 3 = SO 2 ( 3 B 1 ) + O 2 + 35 kcal/mole (1 b ) which form electronically excited SO 2 . No electronically excited O 2 appears to be formed. It is deduced that electronically excited SO 2 is produced by crossing to a separate potential surface at or near the transition state rather than by the formation of a highly vibrationally excited SO 2 molecule which crosses to the excited electronic state.

Deactivation Study of Electronically Excited Cl(2p1/2) Atoms by Socl2 , Ccl3h, C2h4 , No2 Molecules with Laser Magnetic Resonance (Lmr) Technique

2009 ◽  
Vol 4 (4) ◽  
pp. 42-48
Author(s):  
Asylkhan Rakhymzhan ◽  
Pavel Koshlyakov ◽  
Petr Dementiev ◽  
Оleg Aseev ◽  
Alexey Chichinin
Keyword(s):  
Magnetic Resonance ◽  
Quantum Yield ◽  
Ground State ◽  
Room Temperature ◽  
Spin Orbital ◽  
Time Resolved ◽  
Relative Quantum Yield ◽  
Relative Quantum ◽  
Electronically Excited ◽  
Laser Magnetic Resonance

The method of time-resolved laser magnetic resonance (LMR) has been employed to detect spin-orbital excited chlorine Cl*(≡Cl(2P1/2)) atoms at room temperature. The rate constants for the deactivation of Cl* 11 3 10 cm /molecule , 2 s by SOCl2(0.62 0.2), CCl3H (18 5), C2H4(1.5 0.4) and NO2 (1.5 0.4) are reported. The unknown in literature rate constant for the thermo-neutral reaction of ground state Cl(2P3/2) atoms with SOCl2 were measured. The relative quantum yield of Cl* in photodissociation of SOCl2 is determined to be 0.52 ± 0.03.

STUDIES OF CHEMICAL REACTIONS OF EXCITED SPECIES USING INTENSE LIGHT SOURCES

1958 ◽  
Vol 36 (1) ◽  
pp. 102-106 ◽  
Author(s):  
R. A. Marcus
Keyword(s):  
Flash Photolysis ◽  
Excited Molecule ◽  
Inert Gases ◽  
Light Sources ◽  
Adiabatic Temperature Rise ◽  
Misleading Information ◽  
Fluorescence Studies ◽  
Excited Species ◽  
Electronically Excited ◽  
Intense Light

The use of measurements of the products of flash photolysis as a means for studying the reactions of electronically-excited molecules is discussed. With intense light sources the problem of isolating these reactions from others involving free radicals is simplified. The flash sources also have their limitations, and misleading information which can result from the presence of inert gases is noted. A diagnostic test is proposed for detecting the effects (if any) of a possible adiabatic temperature rise of the flash.Some recent studies in the author's laboratory are summarized. Evidence is presented that in the flash photolysis of acetone acetyl radicals arise from an excited molecule. Several deactivation processes are described and compared with results from fluorescence studies.

Fluorescence Quenching of Aminodiphenylamines with Chloromethanes

2002 ◽  
Vol 67 (8) ◽  
pp. 1154-1164 ◽  
Author(s):  
Nachiappan Radha ◽  
Meenakshisundaram Swaminathan
Keyword(s):  
Charge Transfer ◽  
Fluorescence Quenching ◽  
Ground State ◽  
Rate Constants ◽  
Quenching Mechanism ◽  
Quenching Rate ◽  
Charge Transfer Interaction ◽  
Electronically Excited ◽  
A Charge

The fluorescence quenching of 2-aminodiphenylamine (2ADPA), 4-aminodiphenylamine (4ADPA) and 4,4'-diaminodiphenylamine (DADPA) with tetrachloromethane, chloroform and dichloromethane have been studied in hexane, dioxane, acetonitrile and methanol as solvents. The quenching rate constants for the process have also been obtained by measuring the lifetimes of the fluorophores. The quenching was found to be dynamic in all cases. For 2ADPA and 4ADPA, the quenching rate constants of CCl4 and CHCl3 depend on the viscosity, whereas in the case of CH2Cl2, kq depends on polarity. The quenching rate constants for DADPA with CCl4 are viscosity-dependent but the quenching with CHCl3 and CH2Cl2 depends on the polarity of the solvents. From the results, the quenching mechanism is explained by the formation of a non-emissive complex involving a charge-transfer interaction between the electronically excited fluorophores and ground-state chloromethanes.

The Mechanism of the HgH A22Π3/2 → X2Σ+ Emission in the Hg(63P0) Photosensitization of Hydrogen and the Alkanes

1973 ◽  
Vol 51 (8) ◽  
pp. 1207-1214 ◽  
Author(s):  
A. C. Vikis ◽  
D. J. Le Roy
Keyword(s):  
Ground State ◽  
Quantum Yields ◽  
Primary Process ◽  
Relative Quantum

The mechanism of the HgH A22Π3/2 → X2Σ+ emission detected in the Hg(63P0) photosensitized decomposition of H2 and some of the lower alkanes, RH, was investigated. It was concluded that ground state HgH was formed in the primary process Hg(63P0) + RH(or H2) → HgH(X2Σ+) + R(or H). The HgH A22Π3/2 → X2Σ+ emission and presumably the A12Π1/2 → X2Σ+ and B2Σ+ → X2Σ+ emission, also observed in the above systems, result from secondary excitation of ground state HgH on collision with Hg(63P0). Studies of the emission made possible the estimation of relative quantum yields for the above primary process.

Sign in / Sign up

Export Citation Format

Share Document