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We have used the Australia Telescope Compact Array to measure the absorptionfrom the 2(0) - 3(-1}E 12.2 GHz transition of methanol towards the z=0.89lensing galaxy in the PKS B 1830-211 gravitational lens system. Comparison ofthe velocity of the main absorption feature with the published absorptionspectrum from the 1(0) - 2(-1)E transition of methanol shows that they differby -0.6 +/- 1.6 km/s . We can use these observations to constrain the changesin the proton-to-electron mass ratio from z=0.89 to the present to 0.8 +/- 2.1x 10^-7. This result is consistent, and of similar precision to recentobservations at z = 0.68 achieved through comparison of a variety of rotationaland inversion transitions, and approximately a factor of 2 better than previousconstraints obtained in this source. Future more sensitive observations whichincorporate additional rotational methanol transitions offer the prospect ofimproving current results by a factor of 5-10.

First cosmological constraints on the proton-to-electron mass ratio from observations of rotational transitions of methanol