Highly accurate H2 Lyman and Werner band laboratory measurements and an improved constraint on a cosmological variation of the proton-to-electron mass ratio.

Transition wavelengths on a large set of H2 Lyman and Werner band spectral lines have been obtained at an accuracy of 5 x 10(-8), using a narrow band tunable extreme ultraviolet laser. The data are used to determine a constraint on a possible cosmological variation of the proton-to-electron mass ratio (mu=Mp/me) from a comparison with highly redshifted spectral data of quasistellar objects, yielding a fractional change in the mass ratio of Deltamu/mu=-0.5+/-3.6 x 10(-5) (2sigma), which would correspond to a temporal change of d/dt(Deltamu/mu)=-0.4+/-3.0 x 10(-15) per year (2sigma) if a linear cosmological expansion model is assumed.