Rydberg states of propyne at 6.8–10.5 eV studied by two-photon resonant ionization spectroscopy and theoretical calculation

Abstract

The vibronic spectra of jet-cooled propyne at 6.8–10.5 eV have been observed using 2+1 resonance-enhanced multiphoton ionization (REMPI) spectroscopy. The ns (n=4–13), np (n=3–4), and 3dz2 Rydberg states of propyne have been identified, of which seven are newly discovered. The symmetries of the excited vibronic states have been determined directly from polarization-ratio experiments applying linearly and circularly polarized lasers. Under a C3V group, the observed s Rydberg series are of E symmetry and the p Rydberg states belong to A1 or E. Clear doublet splittings in the ns Rydberg states (n=4–9) are observed for the first time. The splittings, 306 cm−1 at 4 s, decrease with increasing n. The doublets of A′ and A″ symmetries, identified from the polarization-ratio measurement, are that due to CS molecular geometry, rather than C3V, for the ns Rydberg states. The term values for the ns Rydberg series (n=6–13) converge to an adiabatic ionization energy of 83 625±2 cm−1 with a quantum defect of δ=0.95. Comparing with one-photon absorption spectrum of propyne, the absence of π→π*, np (n⩾4) and nd (n⩾3, except 3dz2) Rydberg states in the REMPI spectra suggests a strong predissociation character for these states. Calculations for the vertical excitation energies of π→π*, ns, np, and nd (n=3,4) Rydberg states of propyne were performed using time-dependent density functional theory and ab initio methods to compare with experimental results and to test the computational accuracy.

FS+ and FS+(OH−) defect centers at the MgO(100) surface: cluster and periodic calculations

“…Recent studies show that TD-DFT is more accurate than the configuration interaction single (CIS) method [35], and that it can provide transition energies with an accuracy similar to that of multireference configuration interaction or coupledcluster methods [36]. However, Rydberg states [37] and in general transitions to states which are close to the conduction band edge [36] are poorly reproduced.…”

Two-photon vibronic spectroscopy of allene at 7.0–10.5 eV: experiment and theory

“…Following the photodissociation studies of propyne and allene at 193 nm in our laboratory [6,20], we investigated the excited vibronic states of these two molecules at 6.8À10.5 eV using 2 þ 1 resonance-enhanced multiphoton ionization (REMPI) spectroscopy. The two-photon resonance ionization spectrum of propyne has already been published [21]. In this article, we discuss the observed REMPI spectra of allene at 7.0-10.5 eV corresponding to the vibronic transitions of p* p, 3p p, 3d p, 4s p, 4p p, and 4d p, involving valence and Rydberg excited electronic states.…”

“…As discussed for propyne [21], compared with onephoton absorption spectroscopy, the advantages of applying a REMPI laser technique to study the highlying excited electronic states (!6 eV) of polyatomic molecules are as follows. First, the spectral resolution of tunable dye lasers is usually better than that of conventional VUV light source.…”

“…Excited states with fast (pre)dissociation rate, compared to the ionization rate during a multiphoton process, can be excluded from REMPI spectrum unless very high laser power is used. Third, the totally symmetric vibronic excited states can be unambiguously identified from measuring their polarization-ratios, ¼ I circular /I linear , by REMPI spectroscopy [21][22][23]. Fourth, combining with time-of-flight (TOF) mass spectrometry, signal corresponding to a particular mass of interest can be discriminated from other species.…”

Performance of time‐dependent density functional and Green functions methods for calculations of excitation energies in radicals and for Rydberg electronic states

“…Normally, TD‐DFT performs satisfactorily for localized transitions with relatively low excitation energies (∼2–5 eV) but for high‐lying excited states involving delocalized electron distributions and, in particular, for Rydberg states, TD‐DFT tends to underestimate transition energies by up to 1–2 eV 10–14. The excitation energies of Rydberg states can be improved by introducing special ad hoc corrections,15, 17 but these corrections are not universal. Therefore, further development of more sophisticated DFT methods with asymptotically corrected functionals are required.…”