We simulated vertical and NEA phosphorescence of four prototypical chromophores in the gas phase (see Figure ): benzaldehyde (BA), 4-methylbenzaldehyde (MeBA), 4-methoxybenzaldehyde (MoBA), and 4-dimethylaminobenzaldehyde (DMABA). The small size of these molecules and the abundance of previous experimental and theoretical results for BA and its derivatives make them ideal for demonstrating the method. The motivation for choosing these molecules is that the functional groups in the series BA, MeBA, MoBA, and DMABA have an increasing electron donor character, stabilizing the 3 * state, as well known . Thus, we can probe phosphorescence under different relative energies between the 3 n* and 3 * states. The lowest triplet electronic state (T1) of BA can be directly photoexcited , activated via collisional processes , or, more usually, populated after photoabsorption into the singlet manifold . In the latter case, the efficiency of singlet→triplet intersystem crossing is near unity . Thus, BA has weak fluorescence and shows phosphorescence either in a solid matrix or in the gas phase . At zero pressure, the phosphorescence takes between 2 and 4.3 ms . The phosphorescence quantum yield is 0.60, while the T1→S0 intersystem crossing quantum yield is 0.40. The phosphorescence quantum yield decreases on excitation from S0 to S1, S2, and S3 states, indicating competitive relaxation pathways through nonradiative processes in each excited state. Moreover, a triplet excited state (T2) also plays a vital role in quenching S2 and S3