First‐principles simulation of the UV absorption spectrum of ketene

The absorption spectrum of ketene (CH 2 CO) in the 145‐ to 220‐nm region is calculated completely from first principles and compared to a recent high‐resolution synchrotron radiation experiment J Chem Phys 2002, 117, 4306 . The simulations are based on a vibronic model, which is extracted from routinely applicable coupled cluster calculations for electronically excited states. Nonadiabatic effects are assessed by a comparison of the vibronic model simulations with Franck–Condon calculations and are found to be important to understand various aspects of the absorption spectrum of ketene.