A mass and time-of-flight spectroscopy study of the formation of clusters in free-jet expansions of normal D_2

摘要

The mass spectra in the range of 2(D~+)-38(D_(19)~+) amu of clusters formed in a supersonic free-jet expansion of normal D_2 are investigated as functions of source temperature in the range of 95-220 K and of source pressure in the range of 10-120 bars.For some of the small ion fragments,time-of-flight distributions are also measured.For large clusters (n>200) the intensities of the odd-numbered ion fragments exhibit magic numbers at D_9~+and D_(15)~+in accordance with previous experiments and calculations.The even-numbered ion fragments have much smaller intensities and exhibit new magic numbers at D_(10)~+and D_(14)~+.For source conditions such that large clusters are formed,the intensities of the various different ion fragments are observed to saturate beyond a certain source pressure.At lower source pressures,where only small clusters are formed,the terminal mole fractions of the neutral dimers are analyzed in the light of available theories which take into account both the thermodynamics and the kinetics of the expansion.At higher source pressures and lower temperatures,where larger clusters are formed,the sizes of the neutral clusters are estimated using scaling laws and are found to be consistent with the mass spectra and measured time-of-flight distributions.By using a variety of techniques it has been possible to obtain reliable conclusions about the neutral cluster sizes for the present free-jet expansion conditions.