Structural determination and population transfer of 4-nitroanisole by broadband microwave spectroscopy and tailored microwave pulses.

The rotational spectrum of 4-nitroanisole was recorded via chirped-pulse Fourier transform microwave spectroscopy in the frequency range of 2-8 GHz. The spectra of the parent molecule and all of its 13C-, 15N-, and 18O-monosubstituted species in their natural abundance were assigned, and the molecular structure was determined using Kraitchman's equations as well as a least-square fitting approach. 4-nitroanisole has a large dipole moment of 6.15 D along the inertial a-axis and a smaller dipole moment of 0.78 D along the b-axis. The large dipole moment component makes this molecule a potential candidate for deceleration experiments using static electric fields or electromagnetic radiation. Using tailored microwave pulses, we investigate the possibility of transferring population between the rotational states of 4-nitroanisole. Such a technique could be applied to selectively increase the population for specific rotational states of interest, which are then accessible for further, more advanced experiments, such as deceleration.