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We have performed two types of experiments in {\AA} $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}A2\nu 4=1D2CO$: He and self-broadened population decay measurements by transient gain spectroscopy (TGS) on several single rotational levels (SRL's), self-broadened undispersed fluorescence decay measurements on the head. The SRL depopulation measurements allow a comparison between collisional inclastic rotational or vibrational relaxation, enhanced in self-broadening, and collisional electronic quenching, which is a larger fraction of the He-broadened rate. The large irregular variation in He-broadened SRI. depopulation rates indicates that collisional electronic quenching rates vary strongly in a way consistent with the large range of $S1-S0$ matrix elements found by Polik et. al [1]. The fluorescence decay curves at low pressures between 0.9 m Torr and 13.0 m Torr are accurately modeled by single exponential curves with a decay rate linear in pressure, in disagreement with Ref. [2]. At high pressures. the decays become strongly non-exponential. In light of recent measurements on V-V transfer in $\nu 2=1NH3$ (a comparable non-planar system) [3], and of other V-V measurements, we interpret this data with a reversible intersystem crossing model, rather than the V-V model of Ref [4]