Formaldehyde Excited State Optimization

216 Exploring Chemistry with Electronic Structure Methods 

The first job step computes the energies of the three lowest excited states. The second job step uses its results to begin the optimization by including the Read option to the CIS keyword, Geom=Check, and Guess=Read (and of course the commands to name and save the checkpoint file). The Freq keyword computes the frequencies at the optimized structure. 

Here is the stationary point found by the optimization, in its standard orientation  

Unfortunately, the frequency job finds an imaginary frequency, indicating that this structure is not a minimum. Here are the displacements corresponding to this frequency  

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Determine the optimized structure of the first excited state of acrolein, and then compare it to the ground state structure. Compare the change in structure for acrolein to what occurs in formaldehyde. What is the effect of substituting the vinyl group for the hydrogen in formaldehyde ... 

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