Autodetachment spectroscopy Sample Clauses

Autodetachment spectroscopy. To check the assignment of the DBS features, the autodetachment spectrum was examined. This measurement was initially focused on the BeS- (DBS, v = 0) level. Rotational constants for the DBSs of anions are very close to those of the neutral molecule. Using the constant B0 = 0.7873 cm-1 for BeS (X, v = 0) and the observation that the DBS Series2 Series1 Experimental Simulation X0-0 X0-0 X0-0 X0-0 X0-0 X0-0 P 1-1 18600 18675 18750 18825 18900 18975 -1 Transition Energy / cm Figure 3.4. SEVI spectrum of the ν = 0 region of BeS- and simulation (broken red line). The photon energy was 18949.9 cm-1. Figure 3.5: Energy level diagram showing BeS- photodetachment processes. The vertical transitions labeled (i) and (ii) correspond to the features seen at 17910 and 17172 cm-1 in Figure 3 C. Transition (i) is direct photodetachment via the 0 – 1 band, while transition (ii) results in excitation of the BeS- DBS 2+, v = 1 level. Vibrational autodetachment from this level, with N = 0, produces electrons with a kinetic energy of approximately 850 cm-1. Transition (iii) represents excitation of rotational levels of BeS- DBS v = 0 that have sufficient energy to undergo rotational autodetachment. was about 140 cm-1 below the detachment threshold, it was estimated that levels with N  14 would be subject to rotational autoionization. The resulting electrons would have low kinetic energies. To observe these events, the phosphor screen was masked so that only the signal from a central aperture, corresponding to electrons with kinetic energies in the range 0 - 100 cm-1, was registered. This signal was monitored as a function of the excitation laser photon energy. The spectrum obtained is shown in Figure 3.6. The resolution was limited by the laser linewidth, indicating that rotational autodetachment processes were relatively slow. The rotational structure of this band was assigned using upper state combination differences, followed by a fit to the lower state rotational constants and band origin energy by means of the program POPHER.33 The constants obtained from this fit are listed in Table 3.3. Note that the band shows only P- and R-branches, indicating a DBS 2  X 2+ transition. Rotational line assignments are indicated for the 0 – 0 band. Lines of the 1 – 1 band are also present, but they have not been labeled to avoid congestion. The origin of the 0 – 0 band is 141  17 cm-1 below the detachment threshold, where the uncertainty is defined by our measurement of the latt...