The C₃H₇⁺ Appearance Energy from 2-Iodopropane and 2-Chloropropane Studied by Threshold Photoelectron Photoion Coincidence

Abstract

The dissociation onset for halogen atom loss was investigated for 2-iodo and 2-chloropropane ions using a newly developed threshold photoelectron photoion coincidence (TPEPICO) technique that suppresses the effects of hot electrons. This study was undertaken in order to resolve current discrepancies concerning these onsets in the literature. The 0 K dissociation thresholds were determined to be 9.818 ± 0.010 and 11.036 ± 0.010 eV for 2-C 3 H 7 I and 2-C 3 H 7 Cl, respectively. These numbers agree quite well with photoionization and a mass analyzed threshold ionization (MATI) study, but are significantly lower than onsets measured by the much higher resolution pulsed field ionization PEPICO method. The derived C 3 H 7 + heat of formation at 298 K is 803.9 ± 1.5 kJ mol-1 , and a more precise value for the 298 K 2-iodopropane heat of formation is-40.8 ± 1.3 kJ mol-1. The derived proton affinity of propene is 746.1 kJ mol-1. We have also performed a high-level ab initio calculation on the 0 K dissociation limit, E 0 , for C 3 H 7 + from C 3 H 7 Cl at the CCSD(T)/CBS level of theory with high-level corrections. The theoretical prediction of 11.048-11.061 eV for E 0 (C 3 H 7 +) from C 3 H 7 Cl is found to be consistent with the current experimental value.

Accurate ab initio predictions of ionization energies and heats of formation for the 2-propyl, phenyl, and benzyl radicals

“…The AE͑C 3 H 7 + ͒ from 2-C 3 H 7 Cl has been reexamined by employing a higher resolution variant of the threshold photoelectron-photoion coincidence technique based on imaging of near threshold photoelectrons. 19 The latter experiment provided a value of 11.036± 0.010 eV for the AE͑C 3 H 7 + ͒, which is Ϸ40 meV lower than that reported in the PFI-PEPICO study. Using the latter AE value and the known values 46 The present IE prediction for 2-C 3 H 7 radical ͑7.436 eV͒ is 6 meV higher than the experimental value of 7.430± 0.026 eV.…”

“…We note that the ⌬H f0°͑ 2-C 3 H 7 Cl͒ and ⌬H f0°͑ 2-C 3 H 7 ͒ used here have been converted from the literature values ⌬H f298°͑ 2-C 3 H 7 Cl͒ = −144.9± 1.3 kJ/ mol and ⌬H f298°͑ 2-C 3 H 7 ͒ = 87.9± 2.1 kJ/ mol,20 respectively, using the effective anharmonic vibrational frequencies at the CCSD͑T͒/6-311G ͑2df , p͒ level. Similarly, we have obtained the ⌬H f298°͑ 1± 1.6 kJ/ mol 19. As shown inTable II, the CCSD͑T͒/ CBS predictions for the ⌬H f0°͑ ⌬H f298°͒ values in kJ/ mol for…”

“…As shown in Table I 19,20,23,25,[46][47][48][49] for the ⌬H f0°a nd ⌬H f298°o f these neutral and cationic species are also included in Table II for comparison with the theoretical predictions.…”

“…Reliable IE value for the 2-C 3 H 7 radical can be deduced indirectly based on the experimental measurements 19 of the 0 K dissociative photoionization threshold or appearance energy ͑AE͒ for the formation of C 3 H 7 + from 2-C 3 H 7 Cl and the 0 K ͑298 K͒ heat of formation 20 ͓⌬H f0°͑ ⌬H f298°͒ ͔ of 2-C 3 H 7 . The IE for the phenyl radical has been determined with an uncertainty of ±40 meV by photoionization and photoelectron methods.…”

Modeling unimolecular reactions in photoelectron photoion coincidence experiments

“…Therefore, in the last decade, we have embarked on a project to write a PEPICO data analysis computer code that is capable of modeling a wide variety of dissociation mechanisms, including parallel and consecutive dissociations, in linear and reflectron ion time‐of‐flight (TOF) setups, using various rate theories and mechanisms such as tunneling or isomerization. Over the last decade, we have successfully used this program to analyze PEPICO experimental data of the following systems: Simple dissociation C 10 H 15 Cl (chloroadamantane),46 Cp 2 Mn,47 CHCl 2 F,22 (CH 3 ) 2 CO, (CH 3 CO) 2 ,48 t ‐C 4 H 9 NC,49 i ‐C 3 H 7 Br, i ‐C 3 H 7 I,50 CH 2 I 2 , CH 2 Cl 2 , CH 2 Br 2 ,51 C 2 H 3 Br,52 CHCl 3 ,53, 54 (CH 3 ) 3 SiI, (CH 3 ) 4 Si,55 Ge(CH 3 ) 4 ,56 CH 3 NH 2 , C 2 H 5 NH 2 , C 3 H 7 NH 2 , C 4 H 9 NH 2 , i ‐C 4 H 9 NH 2 ,57 (CH 3 ) 3 N, (CH 3 ) 2 NH, (CH 3 )NH 2 ,58 1‐C 4 H 9 I,59 H 2 PC 2 H 5 ,60 CHBr 3 ,54 C 2 H 3 I,61 3‐Cl‐C 3 H 5 , 2‐Cl‐C 3 H 5 ,28 SiCl 4 , SiHCl 3 , SiCl 3 CH 3 , SiCl 3 CH 2 Cl,27 As(CH 3 ) 3 , Sb(CH 3 ) 3 , Bi(CH 3 ) 3 ,26 C 6 H 5 Cl, C 6 H 5 Br, C 6 H 5 I,25 CH 4 ,35 CH 3 I,36 t ‐C 4 H 9 I, t ‐C 4 H 9 OOH,24 C 2 H 5 Br, C 2 H 5 I,29 SCl 2 , SO 2 Cl 2 62 Parallel dissociations ICH 2 CN,63 C 3 H 4 O (acrolein),64 (C 6 H 5 ) 3 COH,65 CH 2 BrI, CH 2 ICl, CH 2 Cl 2 , CH 2 ClBr,51 C 2 H 5 COCH 3 , C 2 H 5 COCOCH 3 ,66 P(CH 3 ) 3 ,67 Ge(CH 3 ) 3 Cl, Ge(CH 3 ) 3 Br,56 neo ‐C 5 H 11 NH 2 ,68 CHCl 2 Br, CHClBr 2 ,54 C 2 H 3 Cl,61 C 3 H 6 ,28 Si 2 Cl 6 , SiCl 3 C 2 H 5 , SiCl 3 C 2 H 3 ,27 (CH 3 ) 4 C,24 t ‐C 4 H 9 OO t ‐C 4 H 9 , t ‐C 4 H 9 NN t ‐C 4 H 9 ,23 (CH 3 ) 2 NNH 2 ,30 Cp 2 Ni, Cp 2 Co, Cp 2 Cr 31…”