Nonradiative transitions in the first excited singlet state of perfluorocyclobutanone: Fluorescence decay times and fluorescence excitation spectroscopy Radiative and nonradiative transitions from the first excited singlet state of methylsubstituted naphthalenes Radiative and nonradiative rates of symmetrically substituted, methylated acetones have been measured in the gas phase. Observed radiative lifetimes are compared to calculated radiative lifetimes obtained from the Strickler-Berg (SB) expression. The calculated values are greater by a factor of 8-9, and an empirical procedure by which the true radiative lifetime can be estimated from the SB expression and the geometry-sensitive correction parameter is given. The rates of nonradiative transitions are reduced appreciably by the a, a' substitution of methyl groups to the C-C-CO-C-C skeleton. The steric crowding introduced by methyl group substitution is considered to be responsible for suppressing the vibrational motion of the promoting modes. In most cases, the S 1 ~ T 1 intersystem crossing predominates over the other nonradiative transitions. rocal disperSion, 5000 A blaze). Light emerging from

Absolute rate constants for the reaction of OH radicals with a series of aromatic hydrocarbons have been determined at room temperature using a flash photolysis-resonance fluorescence technique. The rate constants (& X 1012 cm3 molecule-1 sec-1) obtained are as follows: benzene, 1.24 ± 0.12; toluene, 5.78 ± 0.58; o-xylene, 15.3 ± 1.5; m-xylene, 23.6 ± 2.4; p-xylene, 12.2 ± 1.2; 1,2,3-trimethylbenzene, 26.4 ± 2.6; 1,2,4-trimethylbenzene, 33.5 ± 3.4; 1,3,5-trimethylbenzene, 47.2 ± 4.8. These absolute rate constants are in good agreement with those determined recently for benzene and toluene and with those derived for a series of aromatic hydrocarbons from a relative rate study in an environmental chamber.

Nonradiative transitions in the first excited singlet state of perfluorocyclobutanone: Fluorescence decay times and fluorescence excitation spectroscopy Radiative and nonradiative transitions from the first excited singlet state of methylsubstituted naphthalenes Radiative and nonradiative rates of asymmetric linear aldehydes (C 2 -C 6 ) have been measured in the gas phase. Observe radiative lifetimes are compared to calculated radiative lifetimes obtained from the Strickler-Berg (SB) expression. The calculated values are about the same as the observed values in large aldehydes, but the former is about six times greater than the latter in acetaldehyde. The radiative rates are about four orders of magnitude smaller than the nonradiative rates. The two most important nonradiative processes are S\--! T\ intersystem crossing and type II processes, the latter playing an increasingly important role at high energy in the aldehydes with y·hydrogens. The contrasting radiative behavior of the asymmetric aldehydes from that of the symmetrical ketones is intriguing and suggests important differences in their excited state eqUilibrium geometries and transition moments.

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Rate constants for the reaction of OH radicals with CHF2Cl, CF2Cl2, CFCl3, and H2 have been determined over the temperature range 297–434 °K using a flash photolysis–resonance fluorescence technique. The following Arrhenius expressions were obtained: k1(CHF2Cl) =1.21×10−12e−(3250±300)/RT cm3 molecule−1 sec−1, k1(CF2Cl2) <1×10−15 cm3 molecule−1 sec−1 (T=297–424 °K), k1(CFCl3) <1×10−15 cm3 molecule−1 sec−1 (T=297–424 °K), k1(H2) =5.9×10−12 e−(3990±300)/RT cm3 molecule−1 sec−1. The rate constants for the reaction of OH radicals with H2, which were used to check the experimental system, are in good agreement with literature values. The atmospheric significance of the reaction of OH radicals with CHF2Cl is briefly discussed.