Speaker
Description
Understanding how photoexcited aromatic molecules redistribute energy is central to determining whether excitation leads to photostable relaxation or bond-selective chemistry. Anisole is a model methoxy-substituted aromatic in which bound ππ^states coexist with dissociative πσ^states along the O-CH3 coordinate. Its structured near-ultraviolet absorption band supports bound vibronic levels,¹ whereas methyl elimination is known at higher excitation energies.²˒³ Here, we investigate the early-time dynamics of gas-phase anisole using ultraviolet-extreme-ultraviolet time-resolved photoelectron spectroscopy (UV–XUV TRPES), with excitation at 258, 265, and 278 nm and an approximately 24 eV probe pulse.⁴ At all three wavelengths, the photoelectron signal appears promptly and evolves without abrupt spectral reshaping, delayed continua, or rapid signal loss indicative of prompt transfer to a strongly dissociative state. The response is instrument-response limited at 258 and 265 nm, while excitation at 278 nm shows an additional buildup on an approximately 55 fs timescale. The centre-of-mass of the photoelectron binding-energy distribution exhibits oscillatory modulations arising from coherent vibrational wavepacket motion. Fourier and time–frequency analyses reveal a reproducible component at 930-1030cm-1 across all excitation wavelengths, together with wavelength-dependent contributions at 730-760 cm-1 and weaker features at 1100-1250 cm-1. These coherences decay within approximately 120-160 fs and are assigned predominantly to coupled ring–methoxy motion. Complementary multiconfigurational electronic-structure calculations and surface-hopping simulations indicate confined nuclear motion near the Franck–Condon region or shallow excited-state minima and reproduce vibrational activity in the experimentally observed range. Together, the experimental and theoretical results show that selective excitation between 258 and 278 nm launches coherent vibrational wavepackets within a bound excited-state manifold. Within the temporal window and sensitivity of the measurements, no clear evidence is found for rapid access to the dissociative πσ^*pathway leading to O-CH3 bond cleavage.