Abstract
In this work, we study strong-field molecular alignment in, for the first time, degenerated channels following the same charged states of molecules. By measuring the angular distribution of dissociation fragments from two degenerated N+ + N+ channels of N2, we observe an opposite angular distribution development in these two channels, one expanding and one contracting, when the laser intensity increases. Our further study shows that the expanding channel comes from a nonsequential transition, while the contracting channel involves a sequential transition. We also study the time sequence of the sequential and nonsequential transitions and find that the opposite angular distribution development is due to the different degrees of molecular alignment in these two degenerated channels.
Highlights
In strong laser fields, small molecules can be rapidly aligned with the laser polarization due to the torque on the laser-induced molecular dipole moment[1,2,3,4,5]
While an expansion in the angular distribution profile with increasing intensity has not been commonly seen in previous molecular alignment studies, nor explicit mechanisms have been established[5, 6], it certainly does not indicate a higher degree of alignment in this channel
Previous studies have shown that molecular alignment can be achieved in as fast as tens of femtoseconds for small molecules exposed to intense laser fields[5, 7, 8]
Summary
Small molecules can be rapidly aligned with the laser polarization due to the torque on the laser-induced molecular dipole moment[1,2,3,4,5]. It is of great importance to study the alignment effect in these different dissociation channels of a molecule, since different dissociation channels usually lead to different end products with different kinetic energy and/or residing in different excited states[17,18,19,20,21]. We use these two channels to study, for the first time, strong-field induced molecular alignment effect in degenerated dissociation channels. When we measure the angular distribution of the dissociation fragments as increasing the laser intensity, an opposite angular distribution development is observed in these two channels, one expanding and one contracting. Our further study on the time sequence of the sequential and nonsequential transitions indicate that the opposite angular distribution development is due to different degrees of strong-filed induced molecular alignment in these two degenerated channels
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