## Abstract

Intramolecular vibrational energy relaxation (IVR) is important in many problems in chemical physics. Here, we apply the short-time Fourier transform method for analyzing IVR with classical dynamics. Calculating time-dependent Fourier transforms to perform such an analysis requires extending the usual Fourier transform method, and we do that here. The guiding concept behind the generalization is that if there is a shift of vibrational energy from one frequency range to another, we see a difference between the spectrum before the shift and the spectrum after the shift. We use time-window functions to transform the power spectrum of a trajectory into a time-dependent density spectrum of the average kinetic energy. The time-dependent average kinetic energy for each interval of the spectrum becomes an indicator to monitor the extent and nature of the energy transfer into and out of the corresponding modes. We illustrate this method for the H_{2}O molecule. By analyzing cases with different initial conditions, we show that the short-time Fourier transform method can distinguish trends in IVR that depend on the initial distribution of energy and not just on the total energy.

Original language | English (US) |
---|---|

Pages (from-to) | 3006-3014 |

Number of pages | 9 |

Journal | Journal of Physical Chemistry A |

Volume | 126 |

Issue number | 19 |

DOIs | |

State | Published - May 19 2022 |

### Bibliographical note

Funding Information:This work was supported in part by the National Natural Science Foundation of China (91841301 and 21973053) and by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, under Award DE-SC0015997.

Publisher Copyright:

© 2022 American Chemical Society.