effects such as tunneling through the centrifugal barrier play an important role here. Predicting the collisional properties of a complex molecular system is in general a difficult task, in principle requiring precise calculations of potential surfaces [@PSJ2012]. The number of channels and the density of states in molecular collisions can be very high [@Mayle2012; @Mayle2013], making *ab initio* calculations extremely hard. Therefore a need arises for simple theoretical models able to explain experimental results and make predictions on the collision rates.

One class of such models can be built using the formalism of multichannel quantum defect theory (MQDT) [@Seaton1977; @Fano; @Mies1984a; @Mies1984b; @Julienne1989; @Burke1998; @Gao1998b; @Gao2001; @Gao2005; @Gao2008; @Idziaszek2009a; @Idziaszek2010; @Gao2011; @Ruzic2013; @Gao2013]. This treatment takes advantage of the fact that in many cases the interparticle potential has a known, power-law form ($-C_n/r^n$) at long distances, while the inelastic processes take place only when the particles are very close to each other. The resulting separation of length and energy scales makes the MQDT particularly powerful, allowing to parametrize the short-range physics by the quantum-defect matrix which can be regarded as energy insensitive. If the loss channels are known to have much lesser threshold energies than the entrance channel, the number 