Dieyan Chen

Predissociation of the Na2 3 3Πg and other triplet states

The Na2 3 3Πg state adiabatically dissociates to the 3s+4p atomic limit. The 3 3Πg levels below the 3s+3d atomic limit have been observed by perturbation facilitated optical–optical double resonance (PFOODR) fluorescence excitation spectroscopy. Energy levels above the 3s+3d atomic limit cannot be observed by detecting molecular fluorescence but are observable by detecting atomic 3d→3p fluorescence. The 3 3Πg state interacts with the 3s+3d 2 3Πg state. At lower energy this interaction is responsible for many perturbations between bound vibrational levels of these two states. Above the 3s+3d limit, as a result of this interaction, the 3 3Πg state is strongly predissociated and the linewidths of levels close to the 3s+3d limit are about 22 cm−1. The predissociation interaction is due to an avoided crossing between the adiabatic 2 3Πg and 3 3Πg states at R≈2.85 A. Weak predissociation of the 4 3Σg+ and 2 3Δg states are also observed and discussed.

Doubly excited 1 3∑−g state of Na2: Observation and calculation

The v=0–57 levels of the 3p+3p doubly excited 1 3∑−g state of Na2 have been observed by pulsed perturbation facilitated optical–optical double resonance (PFOODR) fluorescence excitation spectroscopy. The Tv=57=39 943.5 cm−1 of the 1 3∑−g state is 385 cm−1 above the X 2∑+g v+=0, J+=0 ionization threshold and 9 cm−1 below the Na (3p,2P3/2)+Na(3p,2P1/2) dissociation limit. No significant line broadening was observed above the X 2∑+g v+=0, J+=0 ionization threshold with our resolution. Molecular constants and the Rydberg–Klein–Rees (RKR) potential curve have been obtained from the observed data. The major constants are Te=36 519.13(17) cm−1, ωe=93.635(41) cm−1, and Be=0.118 95(90) cm−1. We have carried out an all‐electron ab initio calculation for the 1 3∑−g state and transition dipole moment for the 1 3∑−g↔b 3Πu system of Na2. Molecular constants calculated from our ab initio potential curve have reasonable agreement with the experimental constants.

Predissociation of the Na2 4 3Σg+ state

The Na2 4 3Σg+ state dissociates adiabatically to the 3s+4p atomic limit. The vibrational levels of the 4 3Σg+ state below the 3s+3d atomic limit were observed previously by perturbation facilitated optical–optical double resonance (PFOODR) fluorescence excitation spectroscopy. Vibrational levels above the 3s+3d atomic limit are found to be predissociated and transitions into these levels have been observed by detecting atomic Na 3d→3p fluorescence. The predissociation is due to the interaction with the continuum of the 2 3Πg state (direct as well as accidental predissociation via bound vibrational levels of the 3 3Πg state). The potential energy curve of the 4 3Σg+ state has been constructed.

Molecular constants and Rydberg–Klein–Rees (RKR) potential curve for the Na2 1 3Σg− state

Transitions into the doubly excited Na2 1 3Σg− state have been analyzed using near-dissociation expansions (NDE) to represent the vibrational energies and inertial rotational constants, while the centrifugal distortion constants were held fixed at “mechanically consistent” values calculated from the Rydberg–Klein–Rees (RKR) potential implied by those G(v) and Bv functions. The input data cover the range v=0 to 57 and N up to 47, and the fit yields vD=61.41(±0.10) and D0=3385.70(±0.2) cm−1.