The role of rotational states in IR multiphoton excitation (MPE) is examined for a model spherical top molecule. While the common belief that inclusion of rotational states can enhance MPE by overcoming anharmonic detunings and increasing the number of pathways for excitation is correct for some systems, it is shown that the simultaneous increase in deexcitation pathways can lead to significant rotational heating of lower vibrational bands, and therefore, to a deenhancement of MPE for other systems. The problem of diagonalizing prohibitively large matrices is circumvented by using an artificial intelligence tree pruning algorithm to select the most important basis states for the multiphoton dynamics.
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