Competition Between Two Excitation-dissociation Channels for Molecular Ions

When the molecular ions XYZ＋ （XY2＋） are excited simultaneously from an electronic state E0 into two higher electronic states Ea and EZ with supervened dissociation or predisso- ciation, competition between the α and β excitation-dissociation channels occurs. A the- oretical model is provided to deal with the competition of the two excitation-dissociation channels with more than two kinds of ionic products for XYZ＋ （XY2＋）. Supposing that the photo-excitation rates of two states Eα and Eβ are much less than their dissociation or pre-dissociation rates, a theoretical equation can be deduced to fit the measured data, which reflects the dependence of the product branching ratios on the intensity ratios of two excitation lasers. From the fitted parameters the excitation cross section ratios are obtained. In experiment, we studied the competition between two excitation-dissociation channels of CO^2＋. By measuring the dependence of the product branching ratio on the intensity ratio of two dissociation lasers and fitting the experiment data with the theoretical equation, excitation cross section ratios were deduced.

Effects of geometric configuration on droplet generation in Y-junctions and anti-Y-junctions microchannels

Droplets generation in Y-junctions and anti-Yjunctions microchannels are experimentally studied using a high speed digital microscopic system and numerical simulation.Geometric configuration of a microchannel,such as Y-angle（90°,135°,-90° and-135°）,channel depth and other factors have been taken into consideration.It is found that droplets generated in anti-Y-junctions have a smaller size and a shorter generation cycle compared with those in Yjunctions under the same experimental conditions.Through observing the internal velocity field,the vortex appearing in continuous phase in anti-Y-junctions is one of the key factors for the difference of droplet size and generation cycle.It is found that droplet size is bigger and generation cycle is longer when the absolute angle value of the intersection between the continuous and the dispersed phases（i.e.,the angle between the main channel and the continuous phase or the dispersed phase channel） increases.The droplet＇s size is influenced by the Y-angle,which varies with the channel depth in Y-junctions.The Y-angle has a positive effect on the droplet generation cycle,but a smaller height-width ratio will enhance the impact of a continuous and dispersed phase＇s intersection angle on the droplet generation cycle in Y-junctions microchannels.