**Figure 8.** Rate constants for the photodissociation of the *b* ^{3}Σ^{+} state as a function of the temperature *T*_{*} of the blackbody, for different Maxwell–Boltzmann distribution temperatures *T*_{M − B}. The *T _{MB}* = 2 result, for which only the

**Abstract**

We illustrate some of the difficulties that may be encountered when computing photodissociation and radiative association cross sections from the same time-dependent approach based on wavepacket propagation. The total and partial photodissociation cross sections from the 33 vibrational levels of the *b* ^{3}Σ^{+} state of HeH^{+} towards the nine other ^{3}Σ^{+} and 6 ^{3}Π *n* = 2, 3 higher lying electronic states are calculated, using the autocorrelation method introduced by Heller (1978 *J. Chem. Phys.* **68** 3891) and the method based on the asymptotic behaviour of wavepackets introduced by Balint-Kurti *et al* (1990 *J. Chem. Soc. Faraday Trans.* **86** 1741). The corresponding radiative association cross sections are extracted from the same calculations, and the photodissociation and radiative association rate constants are determined.