Tunneling in a Simple Bond Scission: The Surprising Barrier in the H Loss from HCOOH+

Determination of trace compounds and artifacts in nitrogen background measurements by proton transfer reaction time-of-flight mass spectrometry under dry and humid conditions

A qualitative analysis was applied for the determination of trace compounds at the parts per trillion in volume (ppt_v ) level in the mass spectra of nitrogen of different qualities (5.0 and 6.0) under dry and humid conditions. This qualitative analysis enabled the classification and discovery of hundreds of new ions (e.g., [S_x ]H⁺ species) and artifacts such as parasitic ions and memory effects and their differentiation from real gas impurities. With this analysis, the humidity dependency of all kind of ions in the mass spectrum was determined. Apart from the inorganic artifacts previously discovered, many new organic ions were assigned as instrumental artifacts and new isobaric interferences could be elucidated. From 1140 peaks found in the mass range m/z 0-800, only 660 could be analyzed due to sufficient intensity, from which 463 corresponded to compounds. The number of peaks in nitrogen proton transfer reaction (PTR) spectra was similarly dominated by nonmetallic oxygenated organic compounds (23.5%) and hydrocarbons (24.1%) Regarding only gas impurities, hydrocarbons were the main compound class (50.2%). The highest contribution to the total ion signal for unfiltered nitrogen under dry and humid conditions was from nonmetallic oxygenated compounds. Under dry conditions, nitrogen-containing compounds exhibit the second highest contribution of 89% and 96% for nitrogen 5.0 and 6.0, respectively, whereas under humid conditions, hydrocarbons become the second dominant group with 69% and 86% for nitrogen 5.0 and 6.0, respectively. With the gathered information, a database can be built as a tool for the elucidation of instrumental and intrinsic gas matrix artifacts in PTR mass spectra and, especially in cases, where dilution with inert gases plays a significant role.

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.

Controlling tunnelling in methane loss from acetone ions by deuteration

Methane loss is predominantly a result of quantum tunnelling in acetone cations, and it can be suppressed quantitatively by deuteration.

Effects of collisional and vibrational velocity on proton and deuteron transfer in the reaction of HOD+ with CO

Reaction of HOD(+) with CO was studied over the collision energy (E(col)) range between 0.18 and 2.87 eV, for HOD(+) in its ground state and with one quantum in each of its vibrational modes: (001)--predominantly OH stretch; (010)--bend, and (100)--predominately OD stretch. In addition to integral cross sections, product recoil velocity distributions were also measured for each initial condition. The dominant reactions are near-thermoneutral proton and deuteron transfer, generating HCO(+) and DCO(+) product ions by a predominantly direct mechanism. The HCO(+) and DCO(+) channels occur with a combined efficiency of 76% for ground state HOD(+) at our lowest E(col), increasing to 94% for E(col) around 0.33 eV, then falling at high E(col) to ~40%. The HCO(+) and DCO(+) channels have a complicated dependence on the HOD(+) vibrational state. Excitation of the OH or OD stretch modes enhances H(+) or D(+) transfer, respectively, and inhibits D(+) or H(+) transfer. Bend excitation preferentially enhances H(+) transfer, with no effect on D(+) transfer. There is no coupling of energy initially in any HOD(+) vibrational mode to recoil velocity of either of the product ions, even at low E(col) where vibrational excitation doubles or triples the energy available to products. The results suggest that transfer of H or D atoms is enhanced if the atom in question has a high vibrational velocity, and that this effect offsets what is otherwise a general inhibition of reactivity by added energy. HOCO(+) + D and DOCO(+) + H products are also observed, but as minor channels despite being barrierless and exoergic. These channels appear to be complex mediated at low E(col), essentially vanish at intermediate E(col), then reappear with a direct reaction mechanism at high E(col).

Towards highly accurate ab initio thermochemistry of larger systems: benzene

The high accuracy extrapolated ab initio thermochemistry (HEAT) protocol is applied to compute the total atomization energy (TAE) and the heat of formation of benzene. Large-scale coupled-cluster calculations with more than 1500 basis functions and 42 correlated electrons as well as zero-point energies based on full cubic and (semi)diagonal quartic force fields obtained with the coupled-cluster singles and doubles with perturbative treatment of the triples method and atomic natural orbital (ANO) triple- and quadruple-zeta basis sets are presented. The performance of modifications to the HEAT scheme and the scaling properties of its contributions with respect to the system size are investigated. A purely quantum-chemical TAE and associated conservative error bar of 5463.0 ± 3.1 kJ mol(-1) are obtained, while the corresponding 95% confidence interval, based on a statistical analysis of HEAT results for other and related molecules, is ± 1.8 kJ mol(-1). The heat of formation of benzene is determined to be 101.5 ± 2.0 kJ mol(-1) and 83.9 ± 2.1 kJ mol(-1) at 0 K and 298.15 K, respectively.