Ultrahigh-resolution laser spectroscopy of the S1 1B2u←S0 1Ag transition of perylene

概要

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A rotationally resolved ultrahigh-resolution fluorescence excitation spectrum of the S1 ← S0 transition of perylene has been observed using a collimated supersonic jet technique in conjunction with a single-mode UV laser. We assigned 1568 rotational lines of the 000band, and accurately determined the rotational constants. The obtained value of inertial defect was positive, accordingly, the perylene molecule is considered to be planar with D2h symmetry. We determined the geometrical structure in the S0 state by ab initio theoretical calculation at the RHF/6-311+G(d,p) level, which yielded rotationalconstant values approximately identical to those obtained experimentally. Zeeman broadening of each rotational line with the external magnetic field was negligibly small, and the mixing with the triplet state was shown to be very small. This evidence indicates that intersystem crossing (ISC) in the S11B2u state is very slow. The rate of internal conversion (IC) is alsoinferred to be small because the fluorescence quantum yield is high. Therotational constants of the S1 1B2u state were very similar to those of the S0 1Ag state. The slow internal conversion (IC) at the S1 zero-vibrational level is attributed to a small structural change upon electronic transition.