In our simple model, we assume that the collision rate follows the Wigner threshold law for p -wave inelastic collisions, namely β ∝ T/V 3 / 2 0 , 1 . For large d , V$_{0}$ is significantly smaller than V$_{1}$ , and the loss will proceed predominantly through “head-to-tail” attractive collisions of the polar molecules. In this regime, V$_{0}$ scales as d − 4 and the model predicts that β/T will increase with a characteristic power law of d 6 for d > 0 . 1 Debye [14]. This prediction is in excellent agreement with our measured dependence of the loss rate on d for d > 0 . 1 Debye (Fig. 1 B). For a quantitative description of the inelastic collisional rate over our full range of ex- perimentally accessible dipole moments, we include contributions from both m$_{L}$ = 0 and m$_{L}$ = ± 1 collisions, and we calculate the barrier heights using adiabatic potential curves that include mixing with higher partial waves (see Fig. 2 C). We fit the prediction of this quantum threshold model to our data using a scaling factor, γ , as a free fit parameter, where γ can be interpreted as the loss probability when the collision energy equals the height of the barrier. The resulting theoretical prediction (solid line in Fig. 1) agrees very well with our experimental data (open circles), and we obtain γ = 0 . 35 ± 0 . 08. However, in order to get this agreement over the full range of d , we found it necessary to introduce a second fit parameter that multiplies the coefficient, C$_{6}$ , of the van-der-Waals interaction. The best fit value of this parameter is 1 . 9 ± 0 . 9. Also shown in Fig. 1 B as a dashed line is the result of a more complete quantum scattering calculation that employs a strong absorptive potential at short range but captures the long-range physics and uses C$_{6}$ as the single fit parameter. This fit also agrees well with the experimental data, and gives C$_{6}$ = 21000 ± 7000 a.u. in good agreement with the predicted value of C$_{6}$ = 16130 a.u. [22]. Accompanying the increased inelastic loss rates for increasing d , we observe an increased heating rate for the polar molecule gas. In Fig. 3 we plot the measured initial heating rate as a function of d . The heating rate ˙ T = c is extracted using a linear fit to the measured molecular cloud temperature vs. time, over a time period sufficiently long to allow T to increase by approximately 20 to 30%. In Fig 3, we plot the fractional heating rate ˙ T/T normalized by both the initial n and the initial T . We have developed a simple thermodynamic model for heating that is directly caused by the inelastic loss. We consider the energy lost from the gas when molecules are removed in inelastic collisions, and assume that the gas stays in thermal equilibrium. In this model (see Supplementary Information), the heating arises solely from an“anti-evaporation” mechanism in the trap [23, 24], where 7