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Ionic photofragmentation of carbon monoxide following carbon 1s and oxygen 1s excitation has been measured quantitatively with tuned synchrotron light and time-of-flight mass spectrometry using a Wiley-McLaren apparatus modified with an additional ion lens for improved quantitative performance. The sensitivity of the apparatus to kinetic energy and angular distribution effects has been characterized for selected lens settings through ion trajectory simulations and experimental measurements. Three distinct modes of the added lens have been identified (focus, defocus, and maximum). The focus mode has the least sensitivity to details of the angular and ion kinetic energy distribution and, therefore, is the best mode for measuring quantitative partial ion and ion-pair yields. The defocus mode has the most sensitivity to angular and kinetic energy distributions and, therefore, is the mode that provides the most information about the kinematics of photofragmentation. Branching ratios for ion and ion-pair production in all positive ion fragmentation channels were recorded from 280 to 330 eV (C 1s) and from 520 to 570 eV (O 1s) in the "focus" mode. Quantitative oscillator strengths were derived by combining these branching ratios with absolute total ion yield spectra. The results are compared to literature values.

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Este trabalho estuda a fotofragmentação iônica do metilmetacrilato induzida por radiação síncrotron e por multifotoionização laser. As espécies iônicas foram identificadas por um espectrômetro de massa por tempo de vôo recentemente desenvolvido. No caso da radiação síncrotron tanto fótons com baixa energia (12.1 eV) como fótons com alta energia (287.9 eV) foram utilizados. Apesar da intensidade da fragmentação aumentar com a energia de 12.1 eV até 287.9 eV, o seu padrão permanece basicamente o mesmo e em ambos os casos: o íon pai é facilmente identificável e os fragmentos predominantes são m/q = 15,39,41 e 69. A ionização multifotônica produz bem mais alto grau de fragmentação sendo que o íon pai não foi observado e o espectro é dominado por C + . Os íons m/q = 15, 39, 41 e 69 são detectados tanto utilizando radiação síncrotron como laser evidenciando seu alto grau de estabilidade. Íons com carga dupla não foram detectados.Ionic fragmentation of methylmethacrylate has been observed using synchrotron radiation and laser excitation. A recently developed time-of-flight mass spectrometer was used for the ionic identification. In the case of synchrotron radiation, both low energy (12.1 eV) and high energy (287.9 eV) photons were used. Although a definite increase in fragmentation was observed while moving from 12.1 to 287.9 eV, the fragmentation pattern remained basically the same in both cases. The parent peak stays clearly visible and intense fragments, associated with m/q = 15, 39, 41 and 69 dominate both synchrotron radiation-induced spectra. Multiphoton ionization causes much extensive fragmentation, the parent ion could not be observed, and C + ion becomes the most intense peak in the spectrum. Ions at m/q = 15, 39, 41 and 69 are observed using laser and synchrotron radiation, which demonstrates their high stability. Doubly or multiply-charged ions have not been observed.