Using this model, there are some significant limitations worth noting. For one, only undistorted oscillators are considered; in other words, normal modes without near-identical frequencies are omitted, thereby ignoring any distortion effects. This was probed by Islampour and co-workers , who found that the difference between distorted and undistorted oscillators could be more than several orders of magnitude when it comes to E mn . Orlandi and co-workers noted behaviour similar for the polyacenes, while Andersson and co-workers highlighted that distortion could influence the interpretation of their results. Secondly, the influence of temperature is different when omitting undistorted oscillators. Typically it would be expected that internal conversion approach zero as temperature drops ; that is not the case here. In fact, Andersson and coworkers noted that the observed temperature dependence was minimal with respect to E mn . Minimal temperature effects due to the weak coupling limit agrees with the original tenets of the energy gap law , however it is worth recalling that it is applicable for low temperatures (when the oscillator energy is much larger than the Boltzmann temperature). Thirdly, anharmonic effects are omitted, which are expected to be significant for certain systems. However, in the low-energy scheme, a harmonic model remains valid. In the case of Andersson and co-workers , carotenes can easily be considered within the high-energy regime. Therefore, the internal conversion rate constants for the S 1 → S 0 transition can be expected to shift within an anharmonic model. However, in the case of a derivative series, if the effect is roughly linear, Equation 31 holds. Fourthly, in the case of carotenoids , shifts in the conjugation length of the system, the degree of methyl-substitutions, or the number of -ionone substituents can result in an asymmetry of global constants. In other words, while chemically similar, enough of a difference can be observed in the pre-exponential term leading to misleading results .