title: The fundamental rotational interval of para-H2 (+) by MQDT-assisted Rydberg spectroscopy of H2.
abstract: Transitions from selected nd Rydberg states of H2 to n'p/f Rydberg series converging on the lowest two (N(+) = 0 and 2) rotational levels of the X(+)  (2)Σg (+) (v(+) = 0) ground state of para-H2 (+) have been measured in the range 1-7.4 THz using a laser-based, pulsed, narrow-band source of submillimeter-wave radiation. The analysis of the spectra by multichannel quantum-defect theory (MQDT) has allowed a complete interpretation of the fine structures of the Rydberg series and their dependence on the principal quantum number. The extrapolation of the series to their limits with MQDT has enabled the determination of the first rotational interval of para-H2 (+), which is 174.236 71(7) cm(-1) (5 223 485.1(2.3) MHz).
authors: Laboratorium für Physikalische Chemie, ETH Zürich, 8093 Zürich, Switzerland.
authors: Christa
authors: C
authors: Haase
authors: Laboratorium für Physikalische Chemie, ETH Zürich, 8093 Zürich, Switzerland.
authors: Maximilian
authors: M
authors: Beyer
authors: Laboratoire Aimé Cotton, CNRS, Université Paris-Sud 11, ENS-Cachan, Campus d'Orsay Bâtiment 505, 91405 Orsay, France.
authors: Christian
authors: C
authors: Jungen
authors: Laboratorium für Physikalische Chemie, ETH Zürich, 8093 Zürich, Switzerland.
authors: Frédéric
authors: F
authors: Merkt