ESR of pseudorotating 6Li3 and 7Li3

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Abstract
ESR spectra assigned to pseudorotating 6Li3 and 7Li3 molecules have been produced by arc lamp photolysis of argon matrices doped with isotopically enriched 6Li or 7Li. The spectrum of 6Li3 consists of seven equally spaced first derivative transitions with relative intensities in good agreement with the expected values for three equivalent I=1 nuclei. The measured hf constant and g value are ā=12.21(1) G and go=2.002 82(1). The absence of a stationary trimer spectrum suggests that the ground vibronic state of Li3 is relatively nonlocalized. The average isotropic spin population of the trimer ρ̄=0.225 is in excellent agreement with the predictions of ab initio calculations. The total isotropic spin population 3ρ̄≂0.68 suggests an approximately 30% p‐character for the unpaired electron wave function. A comparison of the orbital composition of M, M2, M3, M∞ (M=Li, Na, K) shows (i) a diminishing s‐character with increasing cluster size, (ii) a remarkable similarity between Na and K for all cluster sizes, and (iii) a smaller s‐character (greater hybridization) for Li clusters.