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 functio n modifications on calculated rotational constants for a set of linear mole cules. These multivariate investigations led to the selection of the MP2/6- 311G* * wave function for a calibrational investigation to predict rotation al constants. The rotational constants predicted by the MP2/6-311G** wave f unctions for the nine training set molecules are 1.3% higher than the exper imental values. Using an appropriate scaling factor the predicted rotationa l constant B-0 value for FC7N is 360.1 MHz. The quality of this prediction is supported by estimates of B-0 for FC5N, HC7N and HC9N, which were not us ed in the calibration set. Predicted B-0 values, 754.1, 564.0 and 290.0 MHz , are in excellent agreement with the experimental ones, 755.4, 564.0 and 2 90.5 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, H C7N and FC7N molecules. (C) 1998 Elsevier Science B.V. All rights reserved.