Varying projection quality of good local electric field gradients of mono-chlorobenzaldehydes

Rotational spectroscopy is an excellent tool for structure determination, which canprovide additional insights into local electronic structure through investigating the hyperfine pattern due to nuclear quadrupole coupling. Jet-cooled molecules are goodexperimental benchmark targets for electronic structure calculations as they are freeof environmental effects. We report the rotational spectra of 2-chlorobenzaldehyde,3-chlorobenzaldehyde, and 4-chlorobenzaldehyde, including a complete experimentaldescription of the nuclear quadrupole coupling constants, which were previously notexperimentally determined. We identified two conformers for 3-chlorobenzaldehydeand one conformer each for 2-chlorobenzaldehyde and 4-chlorobenzaldehyde. Rigorousstructure fitting of 4-chlorobenzaldehyde was performed to determine bond lengths forr$_0$, r$_s$, r$_e$$^{se}$, and r$_m$$^{(1)}$ structures. Comparing experimental nuclear quadupole couplingconstants to computational results showed agreement in the nuclear axis system, butthe accuracy of the projection into the principal axis system decreases in the near-oblate2-chlorobenzaldehyde. The experimental angle Θ$_{az}$ = 19.16◦ between the principal aaxis and nuclear z-axis is larger than predicted by multiple computational methods by≥ 4◦. It is attributed to the high sensitivity of 2-chlorobenzaldehyde to low-energyvibrational contributions.