  We investigate the electric field shielding of ultracold collisions of
dipolar rotors, initially in their first rotational excited state, using an
adimensional approach. We establish a map of good and bad candidates for
efficient evaporative cooling based on this shielding mechanism, by presenting
the ratio of elastic over quenching processes as a function of a rescaled
rotational constant $\tilde{B} = B/s_{E_3}$ and a rescaled electric field
$\tilde{F} = dF/B$. $B, d, F, s_{E_3}$ are respectively the rotational
constant, the full electric dipole moment of the molecules, the applied
electric field and a characteristic dipole-dipole energy. We identify two
groups of bi-alkali dipolar molecules. The first group, including RbCs, NaK,
KCs, LiK, NaRb, LiRb, NaCs and LiCs, is favorable with a ratio over 1000 at
collision energies equal (or even higher) to their characteristic dipolar
energy. The second group, including LiNa and KRb, is not favorable. More
generally, for molecules well described by Hund's case b, our adimensional
study provides the conditions of efficient evaporative cooling. The range of
appropriate rescaled rotational constant and rescaled field is approximately
$\tilde{B} \ge 10^8$ and $3.25 \le \tilde{F} \le 3.8$, with a maximum ratio
reached for $\tilde{F} \simeq 3.4$ for a given $\tilde{B}$. We also discuss the
importance of the electronic van der Waals interaction on the adimensional
character of our study.
