Figure shows cryo-SEVI spectra of H2CCˉ and D2CCˉ along with their peak assignments; blue, black, and red traces are overview spectra, high-resolution composite spectra, and FC simulations, respectively. The high-resolution D2CCˉ spectra show no evidence of spectral broadening beyond that consistent with an unresolved rotational profile, and this is also the case for most features in the H2CCˉ spectrum. However, the situation is more complex upon excitation of the 5 antisymmetric stretch or 6 rocking vibration of H2CC, both of which are non-totally symmetric. The weak 6 0 1 and 6 0 2 peaks in the H2CCˉ spectrum are notably broader than the corresponding peaks in the D2CCˉ spectrum.