The Role of Mass in the Carrier-Envelope Phase Effect for $\rm H_2^+$ Dissociation

The carrier-envelope phase (CEP) dependence of the dissociation of H$_2^+$ is studied with special emphasis on the role of the nuclear mass. We find that the total dissociation probability displays a CEP effect that grows with increasing mass while the difference between dissociating to $p$+H and H+$p$ displays an effect that shrinks. Insight into the physical processes involved is given by an analytic description that casts CEP effects as interferences between pathways requiring different numbers of photons.