Computed photodissociation cross section of the <em>v</em>'' = 5 level of the <em>b</em> <sup>3</sup>Σ<sup>+</sup> state (black) towards the H<sup>+</sup> + He(1s2p <sup>3</sup>P<sup><em>o</em></sup>) channel (red)

<p><strong>Figure 5.</strong> Computed photodissociation cross section of the <em>v</em>'' = 5 level of the <em>b</em> <sup>3</sup>Σ<sup>+</sup> state (black) towards the H<sup>+</sup> + He(1s2p <sup>3</sup>P<sup><em>o</em></sup>) channel (red). The Fourier transform of the autocorrelation not only yields the direct photodissociation cross section (green, full line), but also a contribution from predissociation (green, dotted line) which incorrectly appears as a smooth envelope for short propagation times.</p> <p><strong>Abstract</strong></p> <p>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 <em>b</em> <sup>3</sup>Σ<sup>+</sup> state of HeH<sup>+</sup> towards the nine other <sup>3</sup>Σ<sup>+</sup> and 6 <sup>3</sup>Π <em>n</em> = 2, 3 higher lying electronic states are calculated, using the autocorrelation method introduced by Heller (1978 <em>J. Chem. Phys.</em> <strong>68</strong> 3891) and the method based on the asymptotic behaviour of wavepackets introduced by Balint-Kurti <em>et al</em> (1990 <em>J. Chem. Soc. Faraday Trans.</em> <strong>86</strong> 1741). The corresponding radiative association cross sections are extracted from the same calculations, and the photodissociation and radiative association rate constants are determined.</p>