Spectroscopy of the indium argon van der Waals complex: A high resolution study of the B 2Σ1/2←X2 2Π3/2 system

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Abstract
The InAr van der Waals complex has been characterized by high resolution laser induced fluorescence excitation spectroscopy. Six vibronic bands of the B 2Σ1/2←X2 2Π3/2 transition have been observed and five of these (v′,0), where v′=1–5, have been rotationally analyzed. Rydberg–Klein–Rees potential curves were constructed for the B 2Σ1/2 state using the rotational and vibrational constants determined from these spectra. Equilibrium bond lengths were determined for the B and X2 states and a dissociation energy was determined for the B state. The stronger bonding present in the B state is rationalized in terms of penetration of the argon atom into the diffuse 6s orbital of indium. Evidence is presented that the B state potential energy curve has a barrier at long range, due to Pauli repulsion, of ∼60 cm−1. An analysis of the hyperfine structure involving the 115In nucleus was made. It is concluded that the X2 state conforms to Hund’s coupling case aβ, whereas the B state conforms to case bβs. The extent of 6s–6p hybridization in the upper state was measured from hyperfine splittings and was used in conjunction with a simple electrostatic model to estimate the polarizability of the indium atom in the 6s 2S1/2 state. A value of 68(4) Å3 was obtained (1σ error).