The potential energy surface and dipole moment surfaces of the ã4A2 electronic state of CH2+ are calculated ab initio using an augmented correlation-consistent polarized valence quadruple-ζ (aug-cc-pVQZ) basis set, with the incorporation of dynamical correlation using the coupled cluster method with single and double excitations and perturbatively connected triple excitations [CCSD(T)]. We use these surfaces in the MORBID program system to calculate rotation and rotation–vibration term values for ã-state CH2+, CD+2, and CHD+ and to simulate the rotation and rotation–vibration absorption spectrum of CH2+ in the ã4A2 electronic state. Our work is motivated by studies of CH2+ that use the Coulomb explosion imaging technique and by the goal of predicting spectra that may be obtained from discharge sources. Although the ã state is the lowest-lying excited state above the X̃/àground state pair, it turns out to be relatively high-lying, and we determine that Te(ã)=30447.5 cm−1. The equilibrium bond angle for ã-state CH2+ is only 77.1°; as a result the asymmetric top κ value is close to 0, and the molecule is equally far from the oblate and prolate symmetric top limits in this electronic state.