Primary Photolysis Research Articles

Infrared multiphoton dissociation of DN 3 and HN 3: Formation and reaction of electronically excited ND

Chemiluminescence is observed from DN 3 at pressures below 100 mtorr following irradiation with the focused output of a CO 2 TEA laser. Emission is attributed to ND 2( 2A I) formed in the reaction ND(a 1Δ) + DN 3 → ND 2 ( 2A 1) + N 3. The ND(a 1Δ) is produced in the primary photolysis. Time resolved studies of the fluorescence permit determination of the rate constant for the chemiluminescent reaction (2.09 ± 0.31 μs −1 torr −1). Multiphoton dissociation of HN 3 by use of a laser wavelength coincident with a hot band absorption is also demonstrated.

Absorption spectra and primary photolysis processes of some fluorinated organic compounds in the near and vacuum ultraviolet

Measurements were made of the absorption coefficients of RI=CF3I, C3F7I, CF3CFICF3, and CF3OCF2CF2I in the 120–320 nm spectral range. Investigations were made of the photodissociation processes of CF3OCF2CF2I at λ=254 nm and of the spectral dependences of the main photodissociation processes of RI in the first two vacuum ultraviolet (VUV) bands (155–175 nm). The photodissociation of CF3OCF2CF2I at λ=254 nm with the quantum efficiency Φ1*=1.0−0.05 produced iodine atoms in the first excited state. The main photodecomposition processes of RI in the first VUV band (~160–175 nm) were the predissociation reactions of RI to form R and I(2P3/2) with Φ1=0.76±0.09 (C3F7I) and 1.0±0.1 (CF3I). In the second VUV band the main mechanism of degradation of the excitation energy, at least for the perfluoropropyl iodides, were nonradiative internal conversion processes.

The (b 1Σ+) state of PH in the vacuum ultraviolet photolysis of phosphine

PH (b 1Σ+) has been observed as a primary product in the vacuum ultraviolet photolysis of PH3. The identification has been made from the analysis of some emission bands at 697.3 nm attributed to the transition PH (b 1Σ+→X 3Σ−) and from the measured energy threshold for the excitation of the above bands. The primary photolysis process PH3 (X̃ 1A1) →PH(b 1Σ+) +2H (2S) is consistent with the experimental threshold. The (b 1Σ+) state of PH and the ’’forbidden’’ transition to the ground state have been observed for the first time. The T0 value of PH (b 1Σ+) is 1.78 eV.

Photochemistry of (η-benzene)tricarbonylchromium, tricarbonyl-(η-cyclopentadienyl)manganese, and (η-cyclobutadiene)- and (tris-methylenemethane)-tricarbonyliron in frozen gas matrices at 12 K. Infrared spectroscopic evidence for dicarbonylmetal and dicarbonyl-(dinitrogen)metai complexes

Infrared evidence is presented for the formation of co-ordinatively unsaturated species [ML(CO)2][ML = Cr-(η-C6H6), Mn(η-C5H5), or Fe(η-C4H4), or Fe{C(CH2)H3}] on the u.v. photolysis of [ML(CO)3] complexes in argon and methane matrices, and dinitrogen complexes [ML(CO)2(N2)] in nitrogen matrices at 12 K. The primary photolysis step is readily reversed by visible light for [ML(CO)2] species of Cr and Fe, but not for Mn. The results are discussed in relation to the postulate of co-ordinatively unsaturated species as intermediates in the solution-phase substitution reactions.

The mechanism for ultraviolet photolysis of gaseous chlorine nitrate at 302.5 nm

The laboratory photolysis of chlorine nitrate (ClONO2) with 302.5 nm ultraviolet light leads to the destruction per quantum of 4 molecules of ClONO2 and the formation of 1 molecule of O2, 2 of Cl2 and 2 of N2O5. These quantum yields are not consistent with the current assumption that the primary photolysis step for ClONO2 in the stratosphere leads to the formation of ClO plus NO2. A consistent mechanism exists in which the photolytic step involves the decomposition of ClONO2 to ClONO + O(³P). The onset of observed absorption of radiation by ClONO2 corresponds approximately to the thermodynamic accessibility of this simple splitting away of an O atom.The photolysis of ClONO occurs very rapidly in the stratosphere, either to Cl + NO2 or ClO + NO. The substitution of either Cl + NO2 + O or ClO + NO + O for ClO + NO2 as the eventual photolysis products from ClONO2 is not expected to cause appreciable alteration in predictions from stratospheric modeling.

Photochemical decomposition of EDTA coordinated to cobalt(III): products, thermal reactions, and evidence for outer sphere alcohol oxidation by the excited state

The photolysis of Co(EDTA)− in the ultraviolet is unlike analogous reactions of Fe(III) complexes. The ratio of products Co(II) to CO2 is 1:1 but we find only [Formula: see text] as much CH2O. For Fe(EDTA)−, yields of photolysis products Fe(II):CO2:CH2O are 2:1:1. This is consistent only with a mechanism where primary photolysis yields Co(II), CO2, and a radical which attacks EDTA in preference to reduction of the slowly reducible metal oxidation state, Co(III). Use of 2-propanol as a scavenger diagnostic of primary radicals is questioned because it is shown that LMCT excited states of Co(III) complexes exhibit the same outer sphere oxidations of alcohols earlier recognized in the photochemistry of a variety of Fe(III) complexes.

Processes of photodissociation of free alkyl iodide molecules by 254 nm radiation

The quantum yields of the primary products of the photodissociation of CH3I, C2H5I, C4H9I, CH3CHIC2H5, and (CH3)2CHCH2I were determined in the spectral range 254 nm. It was found that the main primary photolysis process was the splitting off of atomic iodine in the 2Pl/2 excited state and the quantum yield was 0.9, 0.79, 0.67, 0.80, and 0.75, respectively. The quantum yields of the formation of atomic iodine in the 2P3/2 state were 0.1, 0.20, 0.32, 0.09, and 0.24, respectively. Regrouping photodissociation processes producing stable HI and CnH2n molecules (Φ=0.01–0.1) were observed. The quantum yields of other primary photodissociation products were of the order of 2×10–2–10–4.

Photochemistry of tricarbonylnitrosylcobalt in frozen gas matrices at 20 K. Infrared spectroscopic evidence for dicarbonylnitrosylcobalt and dicarbonyl(dinitrogen)nitrosylcobalt

Infrared evidence is presented for the formation of a three-co-ordinate species, [Co(CO)2(NO)], on the u.v. photo-lysis of [Co(CO)3(NO)] in argon and methane matrices.andfortheformationoffour-co-ordinatespecies. [Co(CO)2( N2)(NO)] and probably [Co(CO)(N2)2(NO)], in nitrogen matrices at 20 K. The primary photolysis steps are readily reversed by irradiation with visible light and by annealing the matrix in the case of the reaction of [Co(CO)2(NO)] with CO. The results are discussed in relation to the postulate of co-ordinatively unsaturated and expanded-co-ordination-shell species as intermediates in the thermal substitution reactions of [Co(CO)3(NO)].

Photochemistry of dicarbonyldinitrosyliron in frozen gas matrices at 20 K. Infrared spectroscopic evidence for carbonyldinitrosyliron and carbonyl(dinitrogen)dinitrosyliron

Infrared evidence is presented for the formation of a planar three-co-ordinate species, [Fe(CO)(NO)2], on u.v. photolysis of [Fe(CO)2(NO)2] in argon and methane matrices, and for the formation of four-co-ordinate species, [Fe(CO)(N2)(NO)2] and probably [Fe(N2)2(NO)2] In nitrogen matrices at 20 K. The primary photolysis steps are readily reversed by irradiation with visible light. The results are related to the postulate of co-ordinatively unsatur-ated and expanded-co-ordination-shell species as intermediates in the thermal substitution reactions of [Fe(CO)2(NO)2].

The isothermal flash photolysis of hydrazoic acid

AbstractThe flash photolysis of HN3 was studied by coordinated time‐resolved spectroscopic measurements of HN3 NH(a1Δ), NH(X3Σ), NH(c1π), NH(A3π), NH2, and N3 following flash photolysis of mixtures of HN3 with argon or helium. The primary photolysis is complex, but when the wavelength distribution of the flash is limited to values greater than about 200 nm, the major reactive product is NH(1Δ), or states which quickly decay to NH(1Δ). Disappearance of NH(1Δ) occurs predominantly by the process The process has little, if any, energy of activation, and no detectable dependence on the pressure of inert gas below 1 atm. The rate of formation of NH2 in its ground vibrational state depends on the inert gas pressure in a way that can be accounted for by vibrational relaxation from initial excited vibrational states. The total amount of NH2 is roughly comparable with the amount of HN3 decomposed by primary photolysis. The observed N3 can be attributed to the NH(1Δ) + HN3 reaction, although a smaller amount could also be formed by primary photolysis. The value of k2 is revised upward from the value given in a preliminary report on the basis of a more careful consideration of the effects of Beer's law failure in absorption measurements involving narrow spectral lines.

Photoinduced luminescence of 9,10-anthraquinone. Primary photolysis of 9,10-dihydroxyanthracene

Photoinduced luminescence of 9,10-anthraquinone. Primary photolysis of 9,10-dihydroxyanthracene

Kinetische Prozesse in einem photochemischen Jodlaser * Kinetic Processes in a Photochemical Iodine Laser / Kinetic Processes in a Photochemical Iodine Laser

Abstract Time-dependent gain measurements of a pulsed iodine laser amplifier have been used to deter-mine decay rates of excited iodine atoms 52P1/2 . Rate constants are reported for the iodine deactivation by CF3I and C2F6 . Attempts to correlate the results with predictions from a kinetic model indicate that excited iodine atoms are formed not only in the primary photolysis but also by additional chemical processes.

Flash photolysis of SnCl2 and SnCl4. Dissociation energies of SnCl2 and SnCl

SnCl2 is dissociated to SnCl and Cl by absorption of light in the 320 nm region. This sets a maximum value to the dissociation energy of SnCl2. Further consideration of thermochemical and spectroscopic data gives the probable values of the dissociation energies of SnCl2 and SnCl as 370 ± 20 and 420 ± 20 kJ mol–1 respectively.SnCl2, SnCl, and Sn are observed during the flash photolysis of SnCl4. SnCl2 is produced by decomposition of vibrationally excited SnCl3 formed in the primary photolysis. SnCl is produced by secondary photolysis of SnCl2 and reacts with SnCl4 at a rate approaching the encounter rate. Sn also reacts rapidly with SnCl4.

Chemistry of aliphatic unconjugated nitramines. Part 5.—Primary photochemical processes in polycrystalline RDX

The e.p.r. spectra of polycrystalline RDX, and its single crystals, when irradiated with γ-radiation and 254 nm light at 77–298 K, indicate that ˙NO2 may be a primary photochemical product of RDX. Mass spectral analyses of the gaseous products suggested that N2 and NO may also be primary photolysis products of RDX. The identity of these products was consistent with the theoretically predicted bond cleavage patterns of the axial and equatorial nitramine groups of RDX and HMX. A combination of theory and experiment thus permitted the tentative assignment of the primary photochemical steps for polycrystalline RDX.

Wavelength dependency of the relative proportions of singlet/triplet methylenes from the photolysis of diazomethane

Results of a high pressure study of the photolysis of diazomethane/cis-butene-2/ethylene mixtures at 4358 and 3660 Å under various conditions are reported. These results indicate that the proportion of ground triplet state methylene radicals, produced in the primary photolysis of diazomethane, is independent of photolysis wavelength.

Formation of singlet molecular oxygen from the ozone photochemical system

Photolysis of ozone oxygen mixtures at 2537 Å has been found to produce O 2( 1Σ + g) and O 2( 1Δ g). The O 2( 1Σ g) was produced by energy transfer from O( 1D) and the O 2( 1Δ g) by the primary photolysis step.

Reactions of Nitrogen–Hydrogen Radicals. III. Formation and Disappearance of NH Radicals in the Photolysis of Ammonia

The rates of formation and disappearance of the NH biradical in the ground and first-excited vibrational states were measured by kinetic spectroscopy following flash photolysis of mixtures of ammonia and inert gases. The delay in the appareance of NH following a 25-μsec photolysis flash shows that it is formed by secondary reactions of the primary photolysis products, either NH2 + NH2 or NH2 + H. A large proportion of the observed NH is initially formed in the υ″ = 1 vibrational state, which disappears an order of magnitude faster than NH(υ″ = 0). The disappearance of NH(υ″ = 0) is pressure dependent and in the falloff region at 1 torr, 300°K. The rate of disappearance is rapid and is consistent with NH + NH3 insertion. At the highpressure limit the rate constant for this reaction is k4 = 1.0 ± 0.3 × 1010liter/mole·sec. The reaction has a small negative energy of activation. The high rate of NH disappearance accounts for the small range of conditions under which it can be observed. Implications of the results to the mechanism of biradical insertion reactions are discussed.

Photochemistry of nitroso compounds in solution. V. Photolysis of N-nitrosodialkylamines

N-Nitrosodialkylamines underwent photolysis in the presence of an acid. From the analysis of the end products, the primary photolysis products were shown to be [NOH] and the corresponding alkylideneimine, which underwent further reaction, e.g. (i) recombination of the two species to give amidoximes, (ii) hyponitrous acid formation, and (iii) hydrolysis or polymerization. A pathway is proposed for the reaction. Evidence is presented to show that the formation of the parent amines was not the result of hydrolysis of nitrosamines.

The photolysis of ozone by ultraviolet radiation. I. The photolysis of pure, dry ozone

The photochemical decomposition of dry ozone has been studied at λ = 2537 Å. The quantum yield for the photolysis of pure ozone was proportional to the pressure of ozone; the highest quantum yield recorded was 16.7 at a pressure of 5 cmHg ozone. Variation of light intensity did not markedly affect the quantum yield, and some evidence was found for a wall termination reaction. A reaction mechanism is proposed in which O( 1 D ) atoms, formed in the primary photolysis, initiate a chain propagated by energy-rich oxygen molecules. A discussion of the nature of the energy-rich molecules is presented. Addition of inert gases to the pure ozone reduces the quantum yield to a limiting value of two. This is explained in terms of the deactivation of the energy-rich oxygen molecule. In the presence of oxygen, the quantum yield tends to zero, as a result of the reverse reaction O + O 2 + M → O 3 + M .