Rotational state selection of a CH3I+ ion beam using vacuum ultraviolet-mass-analyzed threshold ionization spectroscopy: characterization using photodissociation spectroscopy

A velocity map imaging study of the photodissociation of the methyl iodide cation

The photodissociation dynamics of the methyl iodide cation has been studied using velocity map imaging and ab initio theory to disentangle the dissociation mechanisms.

Advances in threshold photoelectron spectroscopy (TPES) and threshold photoelectron photoion coincidence (TPEPICO)

The history and evolution of molecular threshold photoelectron spectroscopy and threshold photoelectron photoion coincidence spectroscopy (TPEPICO) over the last fifty years are reviewed.

Bond-dissociation energies of cations--pushing the limits to quantum state resolution

Currently available concepts for measuring the bond-dissociation energy of cations D(o) are reviewed. Starting from the traditional approach of directly measuring the threshold energy for the appearance of fragment ions, attention is directed towards indirect measurements, where threshold energies are obtained by extrapolation of, for example, rate constants k(E) or kinetic energy release (KER) data to the threshold of interest. More recent high precision techniques again utilize direct measurements, for example, of the disappearance energy of the parent ion. Most precise data are obtained from quantum state resolved measurements of the dissociation energy, where the threshold energy is bracketed by the existing quantum states above and below the threshold. Ultimately the limits can even be pushed beyond the bracketing limit, by investigating steps on the lineshape of homogeneously broadened single rotational transitions.

Photodissociation mass spectra and mass-selected resonant (1+1)-photodissociation spectroscopy of some alkyl iodide radical cations

Photodissociation (PD) mass spectra and mass selected (1+1)-photodissociation spectra of C(2)H(5)I(+•), C(2)D(5)I(+•),1- C(3)H(7)I(+•), 2-C(3)H(7)I(+•), 1-C(4)H(9)I(+•) and 2- C(4)H(9)I(+•) radical cations were studied within the à ← X~ absorption band. The photodissociation mass spectra within the range 13,600-15,900 cm(-1) (1.68-1.97 eV) evidence only a simple cleavage of the C-I bond and formation of the corresponding alkyl ions. The resonant (1+1)-photodissociation spectra of C(2)H(5)I(+•) and C(2)D(5)I(+•) show intense vibrational structure in the excited à state. The thresholds for formation of the states of C(2)H(5)I(+•) and C(2)D(5)I(+•) were estimated to be (13,278 ± 12) cm(-1) (1.6462 ± 0.0014 eV)and (13,363 ± 12) cm(-1) (1.6586 ± 0.0014 eV), respectively. Whereas a few resonant vibronic excitations could be identified with 1-C(3)H(7)I(+•) and 1- C(4)H(7)I(+), no vibrational features were observable with 2- C(3)H(7)I(+•) and 2-C(4)H(9)I(+•). It is concluded that 1- and 2-iodoalkane radical cations do not rearrange, even under the conditions of electron ionisation used to generate the molecular ions.

Photodissociation spectroscopy of CD3I+ generated by mass-analyzed threshold ionization for structure determination

A method is devised better to resolve the subbands of the ground vibronic band in the mass-analyzed threshold ionization (MATI) spectrum of CD(3)I. By selective photodissociation of CD(3)I(+) in these subbands, high-resolution spectra for the A(2)A(1)<--X(2)E(3/2) transition are recorded. Spectral analysis confirms our previous suggestion that these subbands are due to cations in different rotational K states; this demonstrates the capability of MATI to generate rovibronically selected ion beams. By using the rotational constants of CH(3)I(+) and CD(3)I(+) obtained by spectral analysis, the zero-point-level geometries of the cations in the X(2)E(3/2) and A(2)A(1) states are determined. To the best of our knowledge, this is the first time that the capability of MATI-PD to determine the geometry of a gas-phase polyatomic cation in an excited electronic state is demonstrated.