Another reason lies in the difficulty to derive accurate structures from ab initio
calculations. One might be tempted to state that today’s computing power should be
sufficient to calculate the structure of any relevant molecule. However, experimentally derived parameters such as the rotational constants are determined with
much higher precision than any possible calculation even for much smaller molecules than mentioned above. Likewise, also perturbative corrections need to be
accounted for in state-of-the-art descriptions of molecules. It is the comprehensive
task of this book to bridge the gap between the accuracy of experimental work and
the versatility as well as speed of theoretical work. Both descriptions are very
detailed and elaborative. The thorough discussion of all the necessary steps to
compare results from both sides will make this book valuable to interested readers
coming from either side of this approach. In this endeavour to establish a bridge
between these two shores, a comprehensive and coherent description of receiving
the accurate structure data of free molecules is achieved.
Stephan Schlemmer
I. Physikalisches Institut
Universität zu Köln
Cologne, Germany
viii
Foreword