Photoionization of propargyl and bromopropargyl radicals: a threshold photoelectron spectroscopic study.

In this Article, we present mass-selected threshold photoelectron spectra of propargyl as well as the 1- and 3-bromopropargyl radicals. The reactive intermediates were produced by flash pyrolysis of suitable precursors and ionized by VUV synchrotron radiation. The TPES of the propargyl radical was simulated using data from a recent high-level computational study.

Time- and frequency-resolved photoionization of the C (2)A(2) state of the benzyl radical, C(7)H(7).

The structure and dynamics of the C (2)A(2) electronically excited state of the benzyl radical, C(7)H(7), were investigated by nanosecond and femtosecond pump-probe photoionization. A free jet of benzyl radicals was generated by flash pyrolysis from the precursors 2-phenylethyl nitrite and toluene. Nanosecond multiphoton ionization spectra show a number of vibronic bands that are excited in the wavelength range of 290-310 nm.

Threshold photoelectron spectroscopy of cyclopropenylidene, chlorocyclopropenylidene, and their deuterated isotopomeres.

Cyclopropenylidene (c-C(3)H(2)), chlorocyclopropenylidene (c-C(3)HCl), and their deuterated isotopomers were studied by the threshold photoelectron-photoion coincidence (TPEPICO) technique using VUV synchrotron radiation. The carbenes were generated via flash pyrolysis. In all species a change in geometry is visible upon ionization, with significant activity in the C═C, C-C-stretching mode and, in the case of c-C(3)H(2)/D(2), the C-H-bending mode.

Threshold photoelectron spectroscopy of the methyl radical isotopomers, CH3, CH2D, CHD2 and CD3: synergy between VUV synchrotron radiation experiments and explicitly correlated coupled cluster calculations.

Threshold photoelectron spectra (TPES) of the isotopomers of the methyl radical (CH(3), CH(2)D, CHD(2), and CD(3)) have been recorded in the 9.5-10.5 eV VUV photon energy range using third generation synchrotron radiation to investigate the vibrational spectroscopy of the corresponding cations at a 7-11 meV resolution.

Side-chain effects on the electronic relaxation of radicals followed by time-resolved pump-probe spectroscopy: 2,3-dimethylbut-2-yl vs tert-butyl.

The excited-state lifetime of the 2,3-dimethylbut-2-yl (DMB) radical, a hexyl isomer, upon electronic excitation into the 3p Rydberg state at 265 nm, is measured by femtosecond time-resolved photoionization. It is shown that the 3p state deactivates in a two-step process, which is well described by two time constants of 25 and 400 fs. The results are compared to tert-butyl (t-C(4)H(9)), another tertiary radical investigated before.

The photoionisation of two phenylcarbenes and their diazirine precursors investigated using synchrotron radiation.

Two phenylcarbenes, chlorophenylcarbene (CPC) and trifluoromethylphenylcarbene (TFPC), were generated by jet flash pyrolysis of diazirine precursors. Their photoionisation was studied by photoelectron-photoion coincidence spectroscopy using synchrotron radiation. For CPC we determined an adiabatic ionisation energy (IE) of 8.

Excited-state lifetime of propadienylidene, l-C3H2.

The excited-state dynamics of the singlet carbene propadienylidene, l-C(3)H(2), were investigated by femtosecond time-resolved photoionisation. The carbene was excited into the C (1)A(1) state with 250 nm pulses and the subsequent excited state dynamics were probed by multiphoton ionization with 800 nm pulses. The lifetime of the C (1)A(1) state was determined to be 70 fs.

Ultrafast dynamics of isolated phenylcarbenes followed by femtosecond time-resolved velocity map imaging.

The ultrafast dynamics of two carbene model systems, chlorophenylcarbene (CPC) and trifluoromethylphenylcarbene (TFPC), has been studied in a molecular beam. Velocity map imaging aids optimizing the pyrolysis conditions for a clean generation of reactive intermediates by supersonic jet flash pyrolysis. The dynamics was followed in real time by time-resolved mass spectroscopy and photoion and photoelectron imaging.

Femtosecond dynamics of isolated phenylcarbenes.

Understanding the primary photophysical processes in molecules is essential for interpreting their photochemistry, because molecules rarely react from the initially excited electronic state. In this study the ultrafast excited-state dynamics of chlorophenylcarbene (CPC) and trifluoromethylphenylcarbene (TFPC), two species that are considered as models for carbene dynamics, were investigated by femtosecond time-resolved pump probe spectroscopy in the gas phase. Their dynamics was followed in real time by time-resolved photoionization and photoelectron imaging.

On the photodissociation of propadienylidene, l-C3H2.

We investigate the photochemistry and photodissociation dynamics of the linear C3H2 isomer propadienylidene by two-colour photofragment Doppler spectroscopy at excitation wavelengths between 260 and 230 nm, corresponding to excitation into the C1 A1 state. Propadienylidene is generated by pyrolysis from IC3H2Br. Almost complete conversion of the precursor can only be achieved at high pyrolysis temperatures.

Photodissociation dynamics of the 2-propyl radical, C3H7.

The photodissociation of 2-propyl leading to propene+H was investigated with nanosecond time resolution. A supersonic beam of isolated 2-propyl radicals was produced by pyrolysis of 2-bromopopane. The kinetic energy release of the H-atom photofragment was monitored as a function of excitation wavelength by photofragment Doppler spectroscopy via the Lyman-alpha transition.

Femtosecond dynamics of the tert-butyl radical, t-C4H9.

The excited-state dynamics of the tert-butyl radical, t-C4H9, was investigated by femtosecond time-resolved photoionization and photoelectron spectroscopy. The experiments were supported by ab initio calculations. tert-Butyl radicals, generated by flash pyrolysis of azo-tert-butane, were excited into the A 2A1 (3s) state between 347 and 307 nm and the 3p band at 274 and 268 nm and ionized by 810-nm radiation, in a [1 + 2'] or [1 + 3'] process.

Excited-state decay of hydrocarbon radicals, investigated by femtosecond time-resolved photoionization: ethyl, propargyl, and benzyl.

The excited state decay of the hydrocarbon radicals ethyl, C(2)H(5); propargyl, C(3)H(3); and benzyl, C(7)H(7) was investigated by femtosecond time-resolved photoionization. Radicals were generated by flash pyrolysis of n-propyl nitrite, propargyl bromide, and toluene, respectively. It is shown that the 2 (2)A(') (3s) Rydberg state of ethyl excited at 250 nm decays with a time constant of 20 fs.