Spectroscopic study of the C 1Σ+ state of 7LiH

Abstract

Forty-two vibrational (v=2–43) levels of the 7LiH C 1Σ+ excited electronic state have been observed by a pulsed optical–optical double resonance fluorescence depletion spectroscopic technique. The absolute vibrational numbering of the C 1Σ+ state is identified with the measurements of the isotopic shifts between 7LiH and 6LiH among several rotation-vibration bands of the C 1Σ+−A 1Σ+ electronic system, and it is further demonstrated by the consistency between observed spectral intensities and calculated ones. The highest observed quasi bound rotational level for the v=43 level is J=8. The spectral term values for those vibrational levels lying above v=33 occur in an irregular order. The level of v=34 lies mainly in the inner, tiny well. The term values for the observed rovibrational levels (2⩽v⩽32, 0⩽J⩽11) in the outer ionic well are described by a set of Dunham-type coefficients, with which a Rydberg–Klein–Rees (RKR) potential energy curve is constructed. This RKR potential is combined with an ab initio potential to construct an effective hybrid potential. The calculated electronic transition moment function for the C-A transition is also given.

Observation of double-well potential of NaH C 1Σ+ state: Deriving the dissociation energy of its ground state

“…The OODR spectrum was detected by monitoring the fluorescence depletion of an X-A transition alternative to the PR pair of the pump laser, i.e., the monochromator detects the Figure 2 shows the fluorescence depletion spectra of the vibrational quantum levels near the dissociation limit of the C state. Successive rovibrational levels C (42, 2-10) were recorded via the intermediate levels A (8,(3)(4)(5)(6)(7)(8)(9)(10). There are some fluorescence-enhanced peaks, e.g., on the traces of the intermediate level A (8,9) or A (8,10).…”

“…Regarding the potential curve of the LiH C 1 Σ + state, which dissociates to Li(3s) + H(1s), a papillose inner potential well is formed due to the effect of the valence and Rydberg atomic configurations, and a major outer potential well is formed due to the interaction between the ionic and neutral electronic configurations. 3 The double-minimum potential commonly exists in the highly excited electronic states as can be seen in the example of LiH 4 and Na 2 . 5 The calculated permanent dipole moments of the NaH C 1 Σ + state exhibits an irregular variation at the avoided crossing regions (2.5, 6.5, and 12.5 Å), which is a well-known magnification of the contribution of covalent and ion-pair a) C.-C. Chu and H.-Y.…”

An optical-optical double resonance experiment in LiH molecules: Lifetime measurements in the C state

“…Among these studies, an optical-optical double resonance ͑OODR͒ experiment has shown that the C state, converging to the Li(3s)ϩH limit, presents a double-well potential shape due to a strong interaction with the Li ϩ uH Ϫ ionic state and local perturbations due to interactions with other neighboring electronic states. 2 These interactions have been theoretically studied by Gemperlé and Gadéa 4 in the frame of a non-BornOppenheimer approximation, involving eight electronic states of 1 ⌺ symmetry. For the highest vibrational levels of the C state, the interaction with the continuum of the A state is dominant and results in strong vibronic shifts, up to 10 cm Ϫ1 , and in nonradiative lifetimes rangs over six orders of magnitude, from nanoseconds to milliseconds.…”

A supersonic beam of cold lithium hydride molecules

“…In 1993, Stwalley and Zemke published a comprehensive review of experimental and theoretical work on the three lowest electronic states of LiH: X 1 Σ + , A 1 Σ + and B 1 Π [15]. More recent studies include extensive sub-Doppler laser spectroscopy of the A-X system [16], high precision studies of the ground-state by emission spectroscopy in the far and mid-infrared [12,17], and the first observation and characterization of the C 1 Σ + state [18,19]. All the experimental studies of gas-phase LiH have used hot sources.…”