Schematic of system showing vibrational structure in the initially prepared state of (left panel); photofragment excitation spectra while probing HCO in , 1, and 2 (middle panel), and a representative density of final HCO states (right panel).
LIF spectra of nascent HCO following excitation of in the state. The upper spectrum shows the overlapping and bands with a simulation of the spectrum shown reflected below. The simulation uses published spectroscopic data for the line positions and fitted populations for the intensities. The lower spectrum shows the spectrum with a similar simulation reflected below.
HCO population distributions following excitation of into four lower-lying states. Predictions of PST are shown as solid lines and provide a reasonable overall interpretation of the data. The interpretation of these data is that all four initial states react following a crossing to the surface.
HCO population distributions following excitation of into two higher lying states. Predictions of PST are shown as solid lines and are a poor model of the data. A single Gaussian function is also shown overlying the data, which provides a better fit. The interpretation of these data is that both initial states react following a crossing to the surface.
HCO population distributions following excitation of into six states that lie between the previous regions. Predictions of PST and the same Gaussian function as Fig. 4 are also shown. Some initial states fit the PST, some fit the Gaussian better, while others seem to be a mixture of the two. These data indicate that both singlet and triplet mechanisms are competitive in this region.
Low resolution HCO LIF spectra following excitation of into the state. These spectra were taken immediately after each other with all experimental conditions kept the same. The spectra are normalized for laser power and are used to calibrate the intensities in high resolution spectra such as Fig. 2.
Product state distributions for HCO in the vibrational state. The populations of the same , states in the state from Figs. 3–5 are shown as a dashed line using the same scale on the population axis. Arrows indicate the maximum allowed in as predicted by PST. In the case of the distributions, this limit is for the states. There are no data for the panel because of interference by the overlapping transition.
distributions for various initial states of in the lower (singlet) and higher (triplet) energy regions. The data are obtained by integrating over , and for each value of . The thin lines indicate the average of the distributions ascribed to the triplet (dashed) and singlet (solid) mechanisms while the heavy line is the prediction of PST. Only low values of could be measured reliably; however, the singlet pathway seems to produce a hotter distribution than the triplet pathway. The dotted line extensions to the data indicate simply that we recognize that the distributions measured here are incomplete.
Six photochemical and photophysical mechanisms for following excitation into the state. Critical energies for each process are indicated.
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