Sensitivity to a possible variation of the Proton-to-Electron Mass Ratio
  of Torsion-Wagging-Rotation Transitions in Methylamine (CH3NH2)
  We determine the sensitivity to a possible variation of the
proton-to-electron mass ratio \mu for torsion-wagging-rotation transitions in
the ground state of methylamine (CH3NH2). Our calculation uses an effective
Hamiltonian based on a high-barrier tunneling formalism combined with
extended-group ideas. The \mu-dependence of the molecular parameters that are
used in this model are derived and the most important ones of these are
validated using the spectroscopic data of different isotopologues of
methylamine. We find a significant enhancement of the sensitivity coefficients
due to energy cancellations between internal rotational, overall rotational and
inversion energy splittings. The sensitivity coefficients of the different
transitions range from -19 to +24. The sensitivity coefficients of the 78.135,
79.008, and 89.956 GHz transitions that were recently observed in the disk of a
z = 0.89 spiral galaxy located in front of the quasar PKS 1830-211 [S. Muller
et al. Astron. Astrophys. 535, A103 (2011)] were calculated to be -0.87 for the
first two and -1.4 for the third transition, respectively. From these
transitions a preliminary upper limit for a variation of the proton to electron
mass ratio of \Delta \mu/\mu< 9 x 10^{-6} is deduced.
