The photodissociation of C&OE\IO, t-(CH3)3CON0, and the clusters [CH3ONO],, with n = 2 to -20, and [(CH3)3CONO],, with n = 2 to -15, was investigated in a supersonic jet using laser excitation to the Sl(nr*) state and 2 + 1 LIF fragment state probing of the N O product including sub-Doppler line profile measurements.We determined the vibrational, rotational, and translational energy distributions as well as the rotational alignment A,+*) and the anisotropy @ of N O emerging from monomer and clusters. The results of CH3ONO in the beam are similar to those found previously in the bulk phase and those of (CH3)3CONO parallel the findings of CH3ON0, implying a decay mechanism which involves direct dissociation and predissociation with the latter being dominant in both molecules. Photodissociation of the weakly bonded [CH3ONO], clusters produces NO fragments with low rotational energy and almost no translational energy = 0; / 3 = 0) but with a vibrational energy distribution equal to that of the monomer. For the stronger bonded cluster [(CH3)3-CONO], also the vibrational excitation of N O is significantly relaxed. On the basis of these results mechanistic features of the cluster photodissociation are proposed.

Ahsorption.s,spektreii, sic,htbar und ultraviolett i Emissionsspektren i Lebenszeiten / QuanterialishruteM Absorption and emission spectra as well as emission quantum yields and lifetimes of 5,lO-dimethylphenazine (DMP), 5-methyl-10-pbenylphenazine, and 5,lO-diphenylphenazine were measured in 3-methylpentane at room temperature and 77' K. By means of relative polarization measurements in conjunction with CND0/2-CI calculations, the excited states were assigned. The long natural lifetime of the fluorescence (TP (DMP) -210 ns), together with the results of the calculation, reveals that the first transition is a symmetry forbidden 'A, --t 'A, transition in a C,, geometry bent along the N -N axis. This transition has an oscillator strength f'" -0.006 for all three compounds as determined from the fluorescence data. We propose that it acquires most of its intensity through a vibronic interaction with S,( 'B,) (Herzberg-Teller coupling). Since intersystem crossing between S,('A,) and T,('A,) is also orbitally forbidden, we suggest, in accordance with the phosphorescence polarization, an electronic spin-orbit coupling between S, and T,. Replacement of the methyl substituents by phenyl groups increases k,,, and enhances the temperature dependent behavior of this parameter. Non-radiative transitions occuring from the lowest triplet state account for nearly 40'%, of the absorbed quanta. Die Absorptions-und Emissionsspektren, die Quantenausbeuten und die Lebenszeiten von 5,lO-Diniethylphenazin (DMP), S-Methyl-10-Phenylphenazin und 5,lO-Diphenylphenazin wurden in 3-Methylpentan sowohl bei RT als auch bei 77 K geniessen. Die Zuordnung der Banden erfolgte anhand der relativen Polarisation in Verbindung mit CND0/2-CI-Berechnungen. Die lange naturliche Lebenszeit der Fluoreszenz ( T : (DMP) -210 ns) und die Recbenergebnisse deuten darauf hin, daR die erste Anregung des um die N-N-Achse gewinkelten Molekiils dem symmetrieverbotenen 'A, --t ' A,(C,,)-Ubergang zuzuordnen ist. Bei allen drei Verbindungen liegt die zugehorige Oszillatorstiirke f", bestimmt aus den Fluoreszenzdaten, in der GroDenordnung von 0,006. Wir nehmen an, daB diese Intensitat in der Hauptsache auf Schwingungswechselwirkungen mit S,( I B,) (Herzberg-Teller-Kopplung) zuruckzufuhren ist. In Anlehnung an die Phosphoreszenzpolarisation und aus dem Verbot des intersystem crossing zwischen S , ( 'A2) und T,(3A,) konnen wir als wahrscheinlich betrachten, daR die elektronische Spin-Bahn-Kopplung zwischen S, und T1 realisiert wird. Parallel zur Zahl der Phenylsubstituenten nimmt k,,, bzw. die Temperaturabhiingigkeit von k,,, zu. Die strablungslosen Uberginge aus dem tiefsten Triplettzustand belaufen sich auf ca. 40 "4 der absorbierten Lichtquanten. bd. 7X. Nr 13 I914

The photoionization and the isothermal recombination luminescence (ITL) of 5,10-dimethylphenazine (DMP), 5-methyl-10-phenylphenazine (MPP), and 5,10-diphenylphenazine (DPP) were investigated in a 3-methylpentane glass at 77 K using a nitrogen laser as the excitation source. The biphotonic nature of the ionization and the particular photophysical properties of these molecules enables one to control the amount of ionization products by simply varying the laser pulse repetition frequency. The slight deviation of the ITL spectra from those of the normal fluorescence and phosphorescence is attributed to differences in the molecular geometry.The ratio of the triplet to singlet molecules, generated following recombination of the electron with the cation, was found to be close to the statistical value of three (DMP: 2.8; MPP: 2.8; DPP: 2.3). From the decay of the ITL the spatial distribution of the trapped electrons around the cations was derived by numerically solving the Smoluchowski equation according to the method of Ichikawa, Yoshida, and Hayashi.

1993 photochemistry, radiation chemistry, chemoluminescence photochemistry, radiation chemistry, chemoluminescence O 0160 20 -088 Photodissociation of Methyl Nitrite CH3ONO, Butyl Nitrite (CH3)3CONO, and the Clusters (CH3ONO)n and ((CH3)3CONO)n. --(KADES, E.; ROESSLEIN, M.; BRUEHLMANN, U.; HUBER, J. R.; J.

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