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The CH3I A-state-assisted photofragmentation of the (CH3I)2 van der Waals dimer at 248 nm and nearby wavelengths has been revisited experimentally using the time-of-flight mass spectrometry with supersonic and effusive molecular beams and the “velocity map imaging” technique. The processes underlying the appearance of two main (CH3I)2 cluster-specific features in the mass spectra, namely, I2+ and translationally “hot” I+ ions, have been studied. Translationally hot I+ ions with an average kinetic energy of 0.94±0.02 eV appear in the one-quantum photodissociation of vibrationally excited I2+(2Π3/2,g) ions (vib=0.45±0.11 eV) via a “parallel” photodissociation process with an anisotropy parameter β=1.55±0.03. Comparison of the images of I+ arising from the photoexcitation of CH3I clusters versus those from neutral I2 shows that “concerted” photodissociation of the ionized (CH3I)2+ dimer appears to be the most likely mechanism for the formation of molecular iodine ion I2+, instead of photoionization of neutral molecular iodine. [ABSTRACT FROM AUTHOR]

Fluorescence decay of gaseous oxalylfluoride (COF)[sub 2] excited to the A˜ [sup 1]A[sub u](7[sup 1]5[sup 1]) level was measured as a function of gas pressure in absence and in presence of magnetic field, B=0.3 T. On excitation to this level, the dynamics in both zero and nonzero fields may be described in the intermediate-molecule limit, with the fluorescence exhibiting biexponential and triexponential decay, respectively. The fast component decay rate constant k[sub f]=(5.31±0.22)·10[sup 7] s[sup -1] is independent on the (COF)[sub 2] gas pressure or magnetic field strength, while that of the first slow component depends on both. The second slow component lifetime is independent of the field strength, while dependent on the gas pressure. The Stern-Volmer dependence, measured with a field in the 0.3-12 mTorr pressure range, is nonlinear. The results obtained were explained by the indirect (electronic- and nuclear-spin-decoupling) mechanism, proposed earlier. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The intermediate LIF spectra were observed and compared in the NO[sub 2] (λ[sub exc]>400 nm) and ClONO[sub 2] (λ[sub exc]=308 nm) photolyses. Both spectra could be assigned to the same transient. Transient fluorescence spectra were recorded in the 12 500-16 400 cm-1 range at λ[sub exc]=436.45 nm. Analysis shows that the observed intermediate spectra can be attributed to the NO[sub 3] radical. The NO[sub 3] lifetime variations in the presence of CF[sub 4], CF[sub 3]Cl, CF[sub 2]Cl[sub 2], CFCl[sub 3], and CCl[sub 4] were also studied. It was shown that these compounds only influence the photolysis yield of NO[sub 3], without affecting its lifetime. The magnetic field influence on the discrete and total NO[sub 2] fluorescence, and on the NO[sub 3] radical yield were also measured using λ[sub exc]=436.45, 458.13, 478.93, and 489.12 nm. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]