Rydberg states of the K2 molecule studied by laser spectroscopy in a supersonic beam

Abstract

Rydberg states of potassium dimer have been studied in a crossed laser-molecular beam experiment. The K 2 molecules were formed in a supersonic expansion and excited by low-power cw dye laser. Two different excitation schemes have been used: The first scheme uses a single mode ring dye laser to induce near resonant two-photon transitions while in the second scheme stepwise excitation with two dye lasers is used. In each case excitation of Rydberg levels was detected by monitoring the ionization signal resulting from three-photon absorption. We report a detailed study of 700 two-photon resonances between 625 nm and 650 nm. Most of these signals can be assigned to transitions from the X 1Sg+ to 1Z~, 1Hg, a n d l a g states, which are all enhanced by the B 1H, intermediate state. Accurate rotational constants are given for the populated vibrational levels of these states. By stepwise excitation of Rydberg levels via the B 1H, state we identify 3 series of Rydberg states as aAg (4S+nD), 1~ (4S+nD), and 1S+ (4S + nS) with principal quantum numbers 7 < n <20. Molecular constants of these and other observed but as yet unidentified states are given; quantum defects and dissociation energies are discussed.

Polarisation Labelling Spectroscopy of Highly Excited (Rydberg)1ΠuStates in Potassium Dimer

“…The RKR potential energy curves calculated using the determined Dunham coefficients are given in Tables II and III. In the absence of theoretical calculations concerning Rydberg states of K 2 (see [22] for the most extensive results) and of direct experimental observations, we can try to assign atomic asymptotes to the observed states only tentatively and by indirect arguments. First, we resort to a general rule that in case of transitions to highly excited molecular states the strongest ones are expected to be those corresponding to the allowed transitions between the asymptotic atomic limits of the molecular states [2,23,24]. Since the observed transitions originate from the ground X 1 Σ + g state, which dissociates to 4s + 4s potassium atoms, it is concluded that the two investigated 1 Π u states correspond to 4s + np and 4s + (n + 1)p asymptotes.…”

“…Most experiments concentrated on states of singlet gerade symmetry, readily accessible via two-step transitions through the well-known intermediate A Π g (4s + nd) to n = 6 [1][2][3][4][5][6][7][8][9] and extrapolation of the longest 1 ∆ g series to n → ∞ provided a reliable value of the molecular ionisation potential [1].…”

Rydberg states of the Li2molecule studied by polarization labelling spectroscopy

“…In the absence of reliable theoretical calculations concerning higher excited states of Li 2 we can try to assign (diabatic) atomic asymptotes to the observed states only tentatively. First, we resort to a general rule that in case of transitions to highly excited molecular states the strongest ones are expected to the states corresponding to the allowed transitions between the asymptotic limits of the molecular states [1,2,19]. Since the observed transitions originate from the ground X 1 Σ + g state, which dissociates to 2s+2s lithium atoms, the three excited 1 Π u states investigated in this work correlate most likely to 2s+np asymptotes.…”