An application of chemometric techniques to the study of ab initio rotational constants of linear molecules

The chemometric techniques Principal Component Analysis (PCA) and two-level Factorial Design (FD) were employed to analyze the effects of wave function modifications on calculated rotational constants for a set of linear molecules. These multivariate investigations led to the selection of the MP2/6-311G** wave function for a calibrational investigation to predict rotational constants. The rotational constants predicted by the MP2/6-311G** wave functions for the nine training set molecules are 1.3% higher than the experimental values. Using an appropriate scaling factor the predicted rotational constant B0 value for FC7N is 360.1 MHz. The quality of this prediction is supported by estimates of B0 for FC5N, HC7N and HC9N, which were not used in the calibration set. Predicted B0 values, 754.1, 564.0 and 290.0 MHz, are in excellent agreement with the experimental ones, 755.4, 564.0 and 290.5 MHz. On the other hand, PLS results using theoretical values for eight wave function predict values of 768.8, 577.7 and 372.3 MHz for the FC5N, HC7N and FC7N molecules.