Tunneling splittings from ab initio data: indoline, a test case

A combination of ab initio and semiclassical modeling is used to simulate the observed tunneling splittings of indoline. Through the Instanton approach and the introduction of effective parameters, the semiclassical one-dimensional theory is extended to the multidimensional case without loss of simplicity. To avoid a possible bias in the derivation of the input parameters, the corrections for the effective mass and the effective potential are obtained ab initio at the standard HF/6-31G∗ level. This framework, which is highly sensitive to the input parameters, successfully reproduces all the observed splittings. Reasons for the success of the present formulation are briefly discussed.