Resonance multiphoton ionization and dissociation of dimethyl ether via the (C)over-tilde, (C)over-tilde and (B)over-tilde states

The three-photon resonance four-photon ionization and dissociation spectra of dimethyl ether (DME) are presented in the wavelength range 450-550 nm at 1 nm intervals. The (3+1) REMPI spectra show three prominent bands corresponding to the (B) over tilde <-- (X) over tilde, <--(C)over tilde> <-- (X) over tilde and (C') over tilde <-- (X) over tilde transitions with origins at 61457 cm(-1) (7.615 eV), 59055 cm(-1) (7.322 eV) and 58010 cm(-1) (7.194 eV), respectively. Several ionized species, CH3+, CHnO+ (n = 1-3) and CH3OCH3+, are observed in the region of wavelengths studied here. In order to compare the results, a shorter wavelength multiphoton dissociation and ionization of DME at 355 nm is also presented. At this wavelength, DME undergoes neutral dissociation to CH3 and CH3O and each fragment is then inonized by multiphoton absorption. The fragmentation at 355 nm is very intense and only small fragments such as CH3+, CHO+, CH2+, CH+ and C+ ions are observed. The measurement of photoelectron energy allows us to establish that the DME ionization potential is at least 9.55 +/- 0.15 eV. The experiments were performed using a Nd:YAG-OPO (optical parametric oscillator) tunable laser system coupled to a time-of-flight mass spectrometer and a hemispherical electron energy analyser.