K. Urbanski

The doubly excited 1 3Σ−g state of 7Li2

This paper reports the first experimental observation of the doubly excited valence (2p+2p)3Σ−g state of 7Li2. We used cw perturbation‐facilitated optical–optical double resonance (PFOODR) fluorescence excitation and resolved fluorescence spectroscopic techniques. All the observed levels have been detected through perturbations by the 2 3Πg state. The deperturbed primary molecular constants of this 1 3Σ−g state are Te=34 045.354(43) cm−1, ωe=216.820(37) cm−1, Be=0.673 69(47) cm−1, Re=2.670 81(94) A, and De=4279.306(43) cm−1. The equilibrium internuclear distance of the 1 3Σ−g state is smaller than that of the X 1Σ+g ground state.

Perturbation facilitated optical–optical double resonance spectroscopy of the 2 3Σ+g, 3 3Σ+g, and 4 3Σ+g Rydberg states of 7Li2

This paper reports the experimental observation of the 2 3Σ+g, 3 3Σ+g, and 4 3Σ+g states of 7Li2 by cw perturbation facilitated optical–optical double resonance spectroscopy. Molecular constants and RKR potential curves have been obtained. Our experimental Te and Re for the 2 3Σ+g state are 27 297.45(16) cm−1 and 3.0797(18) A, respectively, and for the 3 3Σ+g state are 31 043.93(53) cm−1 and 3.0378(19) A, respectively. The above values are in very good agreement with theoretical calculations. Hyperfine splitting for both states has been resolved. Both states follow Hund’s case (bβS) hyperfine coupling scheme. The experimental Fermi contact parameter, bF, is approximately 96±2 MHz for the 2 3Σ+g state and 95.6±3 MHz for the 3 3Σ+g state. These values are in good agreement with the previously obtained value 98.6±4 MHz [Li et al., J. Chem. Phys. 96, 3342 (1992)]. One level of the 4 3Σ+g state has been observed and its hyperfine structure has been resolved and characterized with Hund’s coupling case (bβS).

Hyperfine structures of the 7Li2 b3Πu, 23Πg, and 33Πg states: Continuous wave perturbation facilitated optical–optical double resonance spectroscopy

The hyperfine structure of the b 3Πu, 2 3Πg, and 3 3Πg states of 7Li2 has been studied by continuous wave perturbation facilitated optical–optical double resonance fluorescence excitation spectroscopy. The b 3Πu state has case bβJ coupling scheme. The hyperfine splittings of the two perturbed b 3Πu v=19, N=10, J=11e, s, F1 and v=19, N=5, J=4e, a, F3 levels were resolved and hyperfine constants determined to be +9.90 MHz and −20.94 MHz, respectively. Fermi contact is the main source of the hyperfine interaction and bF(b 3Πu)=+107 MHz has been obtained. The coupling schemes of different 2 3Πg levels are different: N=4, 6 levels observed from the b 3Πu v′=19, N′=5, J′=4e, a, F3 intermediate level and the N=10 levels observed via the b 3Πu v′=19, N′=10, J′=11e, s, F1 intermediate level have case bβJ coupling; the N=5 levels observed via the b 3Πu v′=19, N′=5, J′=4e, a, F3 intermediate level and the N=9, 11 levels observed from the b 3Πu v′=19, N′=10, J′=11e, s, F1 intermediate level are closer to case bβS cou...

All optical triple resonance spectroscopy of the A 1Σ+u state of 7Li2

The A 1Σ+u state of 7Li2 has been studied using all optical triple resonance spectroscopy. Vibrational levels v=27–62 and rotational levels ranging from J=0 to 27 have been observed. This represents a region between previous data from single photon experiments and new data from cold atom photoassociative spectroscopy. Our data was fit to a Dunham expansion and the resulting molecular constants reproduce most observed energies to within 0.050 cm−1. A Rydberg–Klein–Rees potential curve has also been constructed and the calculated eigenvalues are in good agreement with observed energies.

The 2 3Πg and 3 3Πg states of 7Li2: Optical-optical double resonance spectroscopy and ab initio calculations

The (2p+2p) 2 3Πg and (2s+3p) 3 3Πg states of 7Li2 have been studied both experimentally and theoretically. Vibrational levels v=0–41 of the 2 3Πg state and v=6–10 of the 3 3Πg state have been observed by perturbation facilitated optical–optical double resonance (PFOODR) spectroscopy. Our ab initio calculations show that the 2 3Πg state, although dissociating into 2p+2p atomic limit, is a Rydberg state and strongly mixed with the (2s+3p) 3 3Πg and (2s+3d) 4 3Πg Rydberg states. Our theoretical calculations show good agreement with our experimental results.

Predissociation of the F(4) 1Σg+ state of Li2

This paper reports measurements of the homogeneous predissociation of the Li2 F 1Σg+ state due to electrostatic interaction with the E 1Σg+ state. Ab initio potential energy curves have been calculated for both states which in the adiabatic representation show two avoided crossings. However, predissociation was not previously predicted. Our experimental results show that the three isotopomers 7Li2, 6Li7Li, and 6Li2 all strongly predissociate above the 2s+3s atomic limit. We report high resolution measurements of linewidths for a large number of F–state levels spread across the 2600 cm−1 energy region between the 2s+3s and 2p+2p atomic limits, which yield systematic information regarding the rotational, vibrational, and isotopomer dependence of the predissociation rate. An experimental RKR potential energy curve for the F state is derived and used to calculate predissociation rates whose trends show good agreement with the experimental values. This paper presents the first complete data set of observations...

State‐to‐state collision energy transfer of 7Li2 within high‐lying triplet states: Gateway effect of mixed levels in energy transfer between singlet and triplet states

State‐to‐state collision energy transfer in the 2 3Πg, 3 3Πg, 3 3Σ+g, 1 3Σ−g, and 1 3Δg states and from singlet to triplet states of 7Li2 has been studied experimentally by continuous wave optical–optical double resonance (OODR) resolved fluorescence spectroscopy. Propensity rules of collision‐induced transitions within a triplet state have been observed. When a rovibrational (v,J) level of the F 1Σ+g or G 1Πg state was excited by OODR transition, fluorescence from high‐lying triplet gerade states to the a 3Σ+u and/or b 3Πu states was always observed. This indicates that population can transfer from F 1Σ+g and G 1Πg states to triplet states by collision. Irrespective of the J of the initially excited singlet level, the most intense fluorescence from the triplet state will occur at the N or J corresponding to that of the F 1Σ+g (and/or G 1Πg)∼3Λg mixed levels. Molecular population moves to the mixed levels and then transfers to the triplet state. This clearly indicates that singlet–triplet mixed levels pla...

The G 1Πg state of 7Li2 revisited: Observation and analysis of high vibrational levels

CW optical–optical double resonance has been employed to study the upper portion of the G 1Πg state of 7Li2. The use of fluorescence and ion detection enabled the observation of vibrational levels ranging from v=20 to 48 and rotational levels ranging from J=1 to 25. For optical–optical double resonance experiments the Franck–Condon factors between these levels and useful A 1Σu+ state levels (levels that can be reached from the thermally populated levels of the ground state) were exceedingly small. The sensitive ionization detection made possible observation of this upper, anharmonic region of the potential. From the data a Rydberg–Klein–Rees potential curve was constructed which represents over 99% of the potential well depth. A C5 coefficient has been calculated and represents the first experimental determination of a long range coefficient for a doubly excited state in diatomic lithium.