High-resolution photoelectron spectroscopy and calculations of the highest bound levels of below the first dissociation threshold

Abstract

Pulsed-field ionization zero-kinetic-energy photoelectron spectra of D2 have been recorded from the intermediate state to determine the positions of bound rovibronic levels of located within 1400 cm−1 of the D+ + D(1s) dissociation threshold. The ion-pair character of the intermediate state resulted in large changes of the rotational quantum number upon photoionization, which enabled the observation of levels of with rotational quantum number as high as 10. The experimental data cover a range of levels within which the usual hierarchy of timescales of the electronic, vibrational and rotational motions is inverted. The term values of these levels with respect to the X rovibronic ground state of D2 and the energy intervals of the ionic states, measured with an accuracy of typically 0.11 cm−1 and 0.02 cm−1, respectively, are compared with positions calculated ab initio at various degrees of approximation, starting from the Born–Oppenheimer approximation and successively including adiabatic, nonadiabatic, relativistic and radiative corrections. The comparison shows that the accuracy of the photoelectron-spectroscopic measurement is sufficient to reveal the effects of the adiabatic, nonadiabatic, relativistic and radiative corrections on the absolute term values. Comparing our calculations, which rely on an approximate evaluation of the nonadiabatic corrections based on effective R-dependent reduced masses, with the theoretical results for by Moss (1993 J. Chem. Soc. Faraday Trans. 89 3851) and for by Wolniewicz and Orlikowski (1991 Mol. Phys. 74 103) enables the quantification of the errors introduced by our approximative treatment of the nonadiabatic corrections. Improved rotational term values of the level were also derived.