The dissociation energies and mechanism of energy-selected bromo- and iodo-butanes

Vacuum-ultraviolet mass-analyzed threshold ionization spectra of iodobutane isomers: Conformer-specific ionization and ion-core dissociation followed by ionization

“…This is in reasonable agreement with the previously reported value of 8.98Ϯ0.01 eV. 15 Also observed in the MATI spectrum of t-butyl iodide are several sharp peaks associated with ionic vibrational energy levels. Comparison with ab initio calculation ͑MP2/LanL2DZ͒ 16 suggests that the 116, 197, 423, and 535 cm Ϫ1 bands are due to C-I stretching, C-I bending, C-C bending, and C-I stretching/C-C bending combination, respectively.…”

“…Even though the conformer assignment could not be done, we determined the ionization energies to the lower spin-orbit states, which were 73 302 Ϯ5 cm Ϫ1 (9.0883Ϯ0.0006 eV) and 73 326Ϯ5 cm Ϫ1 (9.0913 Ϯ0.0006 eV). These are in good agreement with 9.08 Ϯ0.01 eV reported by Baer and co-workers, 15 Table I. The MATI spectra probing the parent ion or C 4 H 9 ϩ fragment do not show any sharp feature in the threshold region to the upper spin-orbit state. Rather, only broad and structureless bands are observed in both MATI spectra as shown in Fig.…”

“…The appearance energy of 77 770Ϯ150 cm Ϫ1 (9.643Ϯ0.019 eV) thus obtained compares well with the previously reported value of 9.62 Ϯ0.02 eV. 15 The fragmentation threshold is located below the upper spin-orbit state origins by ϳ780 cm Ϫ1 .…”

“…The other possibility is that the fragmentation occurs very slowly in the threshold region such that MATI signals for the parent and fragment coexist even after a long delay time of ϳ20 s after the laser pulse. The appearance energy of the C 4 H 9 ϩ fragment was previously measured to be 9.55Ϯ0.02 eV by PEPICO spectroscopy 15 and is closer to the appearance energy estimated from the fragment MATI signal. Hence, it may be tempting to adopt the second of the explanations above, namely very slow dissociation near the threshold.…”

Photolysis of 1‐C4H9I and 2‐C4H9I at 266 nm: Direct Observation of the Effect of Branching on the Photodissociation Mechanism

“…where E avl is the available energy, E hv the photon energy, D 0 the CÀI bond dissociation energy, evaluated to be 200 kJ mol À1 for 1-C 4 H 9 I [17] and calculated to be 207.5 kJ mol À1 for 2-C 4 H 9 I by using the heat of formation of the radical and parent molecule, [18] E el the electronic energy level of the iodine atom, zero for I and 91 kJ mol À1 for I*, and E p int the internal energy of the parent molecule, which is considered to be zero under the conditions of the supersonic molecular beam. The average translational energy < E t > of each component is calculated from the fitting function.…”