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I would like to know how to effectively induce the bending motion of $\ce{CO_2}$ with femtosecond IR lasers. In other words, how to effectively populate bending vibrational states in $\ce{CO_2}$ neutral or $\ce{CO_2}$ cation?

The ground state of $\ce{CO_2}$ is linear, but the first electronic excited state is bent. Does it mean the bending motion can be more efficiently populated on the electronic excited state? What is the energy gap between the ground state and the first excited state of $\ce{CO_2}$? Is it possible to achieve efficient excitation with a strong IR laser pulse?

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    $\begingroup$ Electronic excitations are pretty much independent of the vibrational ones (though not vice versa). Also, they are way greater in energy than the latter, so you better make up your mind as to whether you want them or not. These would be two entirely different questions. $\endgroup$ – Ivan Neretin Aug 23 '17 at 11:51
  • $\begingroup$ According to Herzberg (Electronic spectra of polyatomic molecules) $\ce{CO2}$ is transparent down to at least $210$ nm and absorbs weekly thereafter. The excited state is bent at 122$^o$ so absorption could excite many vibrational quanta, but transitions from this state to the ground state will result in very highly excited ground state molecules. Your fs IR laser will not be of much use unless you have enough energy and it is short enough (such as can easily produce a continuum) when absorption may be possible by multi-photon effects. However, you may more easily rip the molecule apart. $\endgroup$ – porphyrin Aug 23 '17 at 19:27

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