Spectrum Of The Autoionizing Triplet Gerade Rydberg States Of H-2 And Its Analysis Using Multichannel Quantum-Defect Theory

A new spectrum of the autoionizing triplet states of gerade symmetry of H-2 has been recorded from the upsilon '' = 1-4, N '' = 1-3 rovibrational levels of the metastable c 3 Pi(-)(u) state in a supersonic beam. The spectrum consists of overlapping ns and nd Rydberg series with n in the range between 4 and 45 converging to the upsilon(+) = 1-4, N+ = 0-5 levels of the X+ 2 Sigma(+)(g) ground state of H-2(+). Numerous perturbations caused by s-d and rovibrational channel interactions are revealed in the spectrum and were fully assigned by combining double-resonance experiments and ab initio multichannel quantum-defect theory (MQDT). The energy- and internuclear-distance-dependent eigenquantum-defect parameters of MQDT were derived from available,ab initio calculations of the low-lying electronic states of H-2 and the ground state of H-2(+) and were subsequently refined in a global fit to experimental data. The positions of 552 triplet ns and nd Rydberg levels of H-2 (361 of which were measured in the present study) could be reproduced with a root-mean-square deviation of 0.2 cm(-1).