The rotationally resolved infrared photodissociation spectrum of Cl−-HD is measured in the HD stretch region. Two Σ-Σ bands are observed, corresponding to transitions from the ground state [the (vHD = 0, n = 0) level] and first excited intermolecular bend state [the (vHD = 0, n = 1) level]. The (vHD = 0, n = 0) and (vHD = 0, n = 1) states are predominantly associated with the linear Cl−⋯DH and Cl−⋯HD geometries, respectively. The spectrum is complicated by perturbative interactions between levels of the (vHD = 0, n = 0) and (vHD = 0, n = 1) rotational manifolds and between levels of the (vHD = 1, n = 0) and (vHD = 1, n = 1) rotational manifolds. A global fit to the transition frequencies, taking the lower and upper state perturbations into account, yields zero-order rotational and centrifugal distortion constants and allows us to establish that the (vHD = 0, n = 1, J″ = 0) level lies 13.7 cm−1 above the (vHD = 0, n = 0, J″ = 0) level. Rovibrational energy level calculations performed using a recent ab initio potential energy surface confirm the picture emerging from the experimental data and provide good agreement with measured molecular parameters. The results emphasize the importance of quantum mechanical interconversion between two isomeric structures of a simple anion complex. © 2004 American Institute of Physics.