Dissociative electron attachment in cyclopentanone, γ-butyrolactone, ethylene carbonate, and ethylene carbonate-d4: Role of dipole-bound resonances

Phys. Chem. Chem. Phys.

Monney

et al. 2007

Self Cite

104

127

We studied dissociative electron attachment to a series of compounds with one or two hydroxyl groups. For the monoalcohols we found, apart from the known fragmentations in the 6-12 eV range proceeding via Feshbach resonances, also new weaker processes at lower energies, around 3 eV. They have a steep onset at the dissociation threshold and show a dramatic D/H isotope effect. We assigned them as proceeding via shape resonances with temporary occupation of s * O-H orbitals. These low energy fragmentations become much stronger in the larger molecules and the strongest DEA process in the compounds with two hydroxyl groups, which thus represent an intermediate case between the behavior of small alcohols and the sugar ribose which was discovered to have strong DEA fragmentations near zero electron energy [S. Ptasin´ska, S. Denifl, P. Scheier and T. D. Ma¨rk, J. Chem. Phys., 2004, 120, 8505]. Above 6 eV, in the Feshbach resonance regime, the dominant process is a fast loss of a hydrogen atom from the hydroxyl group. In some cases the resulting (M À 1) À anion (loss of hydrogen atom) is sufficiently energyrich to further dissociate by loss of stable, closed shell molecules like H 2 or ethene. The fast primary process is state-and site selective in several cases, the negative ion states with a hole in the n O orbital losing the OH hydrogen, those with a hole in the s C-H orbitals the alkyl hydrogen.

Section: Methodsmentioning

confidence: 99%

Electron-induced chemistry of alcohols

Phys. Chem. Chem. Phys.

Monney

et al. 2007

Self Cite

104

127

“…[20][21][22] It employs a magnetically collimated trochoidal electron monochromator 23 to prepare a beam of quasi-monoenergetic electrons, which is directed into a target chamber filled with a quasi-static sample gas. Fragment anions are extracted at 901 by a three-cylinder lens and directed into a quadrupole mass spectrometer.…”

Section: Methodsmentioning

confidence: 99%

“…33,34 A more recently discovered case is C 60 (reference 35 and references therein)-but it is not comparable to the present case because the long-term electron attachment occurs over a very wide range of energies, not via a specific resonance. A relevant example where a search for a long-lived anion with the full molecular mass failed is g-butyrolactone, 20,32 illustrated in the scheme in Fig. 5.…”

mentioning

confidence: 99%

Cleavage of the ether bond by electron impact: differences between linear ethers and tetrahydrofuran

Phys. Chem. Chem. Phys.

Allan

2008

Self Cite

Dissociative electron attachment (DEA) to diethyl ether yielded primarily the C 2 H 5 O À ion, with a strong Feshbach resonance band at 9.1 eV and a weaker shape resonance band at 3.89 eV. Very similar spectra were obtained for dibutyl ether, with C 4 H 9 O À bands at 8.0 and 3.6 eV. Some of these primary ions subsequently lost H 2 and yielded weaker signals of the C 2 H 3 O À and C 4 H 7 O À ions. In contrast, DEA to the cyclic ether tetrahydrofuran (THF) yielded mainly a fragment of mass 41, presumably deprotonated ketene, at 7.65 eV. The low-energy band was missing in THF. H À with two bands at 6.88 and 8.61 eV, and an ion of mass 43 (presumably deprotonated acetaldehyde) with two bands at 6.7 and 8.50 eV were also observed. We propose that in the primary DEA step the C-O bond is cleaved in both the open-chain and the cyclic ethers. In the open-chain ethers the excess energy is partitioned between the (internal and kinetic) energies of two fragments, resulting in an RO À ion cool enough to be observed. The CH 2 (CH 2 ) 3 O À ion resulting from cleavage of the C-O bond in THF contains the entire excess energy (more than 6 eV at an electron energy of 7.65 eV) and is too short-lived with respect to further dissociation and thermal autodetachment to be detected in a mass spectrometer. These findings imply that there could be a substantial difference between the fragmentation in the gas phase described here and fragmentation in the condensed phase where the initially formed fragments can be rapidly cooled by the environment.

“…17,36 It employs a magnetically collimated trochoidal electron monochromator to prepare a beam of quasi-monoenergetic electrons which is directed into a target chamber filled with a quasi-static sample gas. Fragment anions are extracted at 901 by a three-cylinder lens and directed into a quadrupole mass spectrometer.…”

Section: Methodsmentioning

confidence: 99%

“…Representative examples are CH 3 I, 15 N 2 O 16 and ethylene carbonate. 17 The VFR mechanism has been shown to be operative in uracil and thymine. 7,18 In virtually all compounds one or several DEA bands are also found in the 5-14 eV range.…”

Section: Introductionmentioning

confidence: 99%

Electron-induced chemistry of alcohols

Allan

2008

J. Phys.: Conf. Ser.

We studied dissociative electron attachment to a series of compounds with one or two hydroxyl groups. For the monoalcohols we found, apart from the known fragmentations in the 6-12 eV range proceeding via Feshbach resonances, also new weaker processes at lower energies, around 3 eV. They have a steep onset at the dissociation threshold and show a dramatic D/H isotope effect. We assigned them as proceeding via shape resonances with temporary occupation of s * O-H orbitals. These low energy fragmentations become much stronger in the larger molecules and the strongest DEA process in the compounds with two hydroxyl groups, which thus represent an intermediate case between the behavior of small alcohols and the sugar ribose which was discovered to have strong DEA fragmentations near zero electron energy [S. Ptasin´ska, S. Denifl, P. Scheier and T. D. Ma¨rk, J. Chem. Phys., 2004, 120, 8505]. Above 6 eV, in the Feshbach resonance regime, the dominant process is a fast loss of a hydrogen atom from the hydroxyl group. In some cases the resulting (M À 1)À anion (loss of hydrogen atom) is sufficiently energyrich to further dissociate by loss of stable, closed shell molecules like H 2 or ethene. The fast primary process is state-and site selective in several cases, the negative ion states with a hole in the n O orbital losing the OH hydrogen, those with a hole in the s C-H orbitals the alkyl hydrogen.