The phosphorescence spectrum of gaseous propynal (HCCCHO) is measured by time-resolved techniques following pulsed (1 via direct optical pumping into the S0 → T1 absorption transition and (ii) four single vibronic levels (SVL) of S1 (O0, 61, 41, and 21). The time-resolved emission is identified as T1 → S0 phosphorescence by its appearance at microsecond delays after excitation, its relative frequency shift (2039 cm-1) to lower energy from the 00 0 transition observed for fluorescence, and the assignment of vibronic structure to transitions involving vibrational modes in T1. The phosphorescence spectrum observed after direct optical excitation of T1 contains a simple vibronic structure having activity primarily in ν″4 with significantly weaker bands assignable to transitions to ν″9 and ν″12. The same vibronic structure is recorded in the phosphorescence measured following SVL excitation into S1, except that several new transitions originating from excited vibrational levels of T1 appear. Phosphorescence from these excited vibrational levels (having as much as 385 cm-1 of excess vibrational energy) reflect the room-temperature thermalization which occurs following intersystem crossing from S1 and vibrational relaxation within T1.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Atomic and Molecular Physics, and Optics