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The K-MM radiative-Auger transition probabilities for Ca, Ti and Cr were calculated using time-dependent perturbation theory. The atom plus the free radiation field are considered as being one system and the transition of one state of the atom to another results from the interaction between components of this system. The perturbing Hamiltonian is taken as the sum of the interaction between the electrons participating directly in the process and their interaction with the radiation field. Under this approach, the radiative-Auger process is described considering second-order terms in time-dependent perturbation theory series. The calculations were performed using screened hydrogenic wavefunctions to describe the state of the atom. The results obtained are compared with recent experimental data and other theoretical calculations.

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A time-to-digital converter coupled to a charge-to-digital converter has been used to record mass spectra in matrix-assisted laser desorption (MALD) time-of-flight mass spectrometry. Masses above 100 000 Da have been detected by ion counting. Utilizing an electrostatic mirror, good mass resolution has been achieved in MALD. When the number of detected secondary ions is small the sensitivity of mass measurements is improved by using a charge-to-digital converter rather than a transient recorder.Time-of-flight (TOF) mass spectrometry is a very useful method for the study of large proteins and molecular clusters. The new technique of matrix-assisted laser desorption (MALD), suggested by Karas and Hillenkamp,' and by Tanaka et al. ,' is very promising and requires modest experimental facilities. However, the full utilization of the MALD technique for analytical purposes still depends on improvements in mass resolution , mass accuracy, and detection efficiency of large molecular ions.The present experiments were performed in order to gain an understanding of some aspects of the laser desorption mechanism (fragmentation, cluster emission, etc.) and also to evaluate the potential of a new electronic timing device in time-of-flight spectrometry. Several kinds of samples were investigated using different analytical procedures. The molecular mass range of the proteins studied was between -1000 and 70 000 Da. In some cases it was possible to observe the desorption of large clusters of protein molecules. The enhancement of the desorption yield of these large clusters strongly depends on the procedure adopted for sample and target preparation.Different kinds of electronic devices have been developed at the Institut de Physique NuclCaire (IPN) at Orsay, for the time-of-flight mass spectrometer TOF 23.3 Results obtained with a conventional time-todigital converter (TDC) are compared with results obtained using a TDC coupled to a charge-to-digital converter (CDC). The CDC measures the total electric charge associated with each signal of secondary ions arriving on the stop detector (stop signal). This total charge is thus proportional to the number of ions simultaneously hitting the detector. The charge is converted to a digital value which is added to the TOF mass spectrum at the corresponding time value measured by the TDC. A transient waveform recorder has also been used and the results obtained compared with those obtained with the TDC and CDC.It was observed that the mass resolution decreases with the power density of the irradiating laser beam.