Implications of comparative spectral doublets observed for neon-isolated and gaseous tropolone(OH) and tropolone(OD)

Spectral doublet separations reported for gas phase and neon matrix-isolated samples of tropolone(OH) and tropolone(OD) are found to support recent work suggesting the possibility that tropolone has a slightly nonplanar geometry in the S1 (A 1B2) (pi*-pi) electronic state. Tautomerizations of gaseous tropolones in the S0 and S1 states are governed by equal double-minimum potential energy functions (PEFs), but interactions in the neon matrix environment transform the tautomerization PEFs of the slightly nonplanar S1 tropolones into unequal double-minimum PEFs. The spectral doublets reported for the zero-point S1-S0 transitions imply energy minima for the nonplanar S1 state in a neon matrix are offset by about 7 cm-1, and tunneling splittings in the symmetric double minimum PEFs of the gaseous molecules are damped about 2 cm-1 by the matrix environment. This means gas phase tunneling splittings smaller than 2 cm-1 are fully quenched in the neon matrix, and gas phase tunneling splittings near 20 cm-1 are damped by only 10%.