•Protonated carbon monoxide e–IDR rates agree with previous measurements.•The current H12CO+/D12CO+ ratio agrees with previous experimental measurements.•The addition of 13C to protonated carbon monoxide decreases the e–IDR rate constant.•Flowing afterglow measurement of protonated formaldehyde.The room temperature electron–ion dissociative recombination (e–IDR) rate constants (αe) for the isotopomers of protonated carbon monoxide (HCO+) and protonated formaldehyde (H3CO+) have been measured using a flowing afterglow equipped with an electrostatic Langmuir probe. The isotopomers included in this study and their corresponding e–IDR rate constants are H312CO+, 7.4 × 10−7 cm3 s−1; H313CO+, 6.8 × 10−7 cm3 s−1; H12CO+, 2.0 × 10−7 cm3 s−1; H13CO+, 1.8 × 10−7 cm3 s−1; D12CO+, 1.6 × 10−7 cm3 s−1; and D13CO+, 1.4 × 10−7 cm3 s−1. The recombination rate constants for the measured isotopomers exhibit a decrease in the rate constant with the addition of a heavy isotope. This effect is greater with a hydrogen/deuterium substitution than with a 12C/13C substitution. The comparison of the current data with previously published data is discussed.

Recently, methyl formate, glycolaldehyde, and acetic acid have been detected in the Interstellar Medium, ISM. The rate constants, αe, for dissociative electron–ion recombination of protonated gycolaldehyde, (HOCH2CHO)H+, and protonated methyl formate, (HCOOCH3)H+, have been determined at 300 K in a variable temperature flowing afterglow using a Langmuir probe to obtain the electron density. The recombination rate constants at 300 K are 3.2 × 10–7 cm3 s–1 for protonated methyl formate and 7.5 × 10–7 cm3 s–1 for protonated glycolaldehyde. The recombination rate constant of protonated acetic acid could not be directly measured, but it appears to have a rate constant, αe, on the 10–7 cm3 s–1 scale. Several high- and low-temperature measurements for protonated methyl formate were made. In addition, an αe measurement at 220 K for protonated glycolaldehyde was performed. The astrochemical implications of the rates of recombination, αe, and protonation routes are discussed.

Electron–ion dissociative recombination rate constants have been determined for protonated single six-membered hydrocarbon rings with varying N-atom substitution in the rings and varying degrees of methyl substitutions to the rings. The species studied have been protonated forms of the xylenes (C8H10; with configurations o, m, and p), the picolines (C6H7N; with methyl substitutions located at 2, 3, and 4), mesitylene (C9H12) and 2, 5-lutidine (C7H9N). By operating at high reactant vapor pressures, ternary association has been made to dominate over recombination to create proton bound dimers and the rate constants of these species have been determined. The studies were made at room temperature in a flowing afterglow with a Langmuir probe to determine the reduction in electron density as a function of distance along the flow tube. All of the data except for mesitylene showed a consistent trend with the numbers of N-atom substitutions and CH3 attached to the rings. For the protonated species, the rate constants increase with the number of nitrogens and decreased with number of CH3 substituents attached to the ring. For proton bound dimers, the rate constants increase with both, the number of N-atoms and number of CH3 substituents. For the xylene and picoline isomer's the measurements showed that the rate constants were independent of isomeric form, and thus, it is not necessary to study all isomeric forms. The relevance of these studies to the ionosphere of Titan is discussed.Graphical abstractHighlights► Protonated ring rates increase with number of nitrogens within the ring. ► Protonated ring rates decrease with the number of methyl additions. ► Proton bound ring dimers have the opposite effect of the protonated forms. ► Isomeric form has little effect on the rate.

The rate constants, αe, for dissociative electron–ion recombination of various isotopic combinations of N2H+ have been determined at 300 and 500 K in a variable temperature flowing afterglow using a Langmuir probe to determine the electron density. The values of αe at 300 K are 2.77 (14N2H+), 2.12 (14N2D+), 2.31 (15N2H+) and 1.98 (15N2D+) × 10−7 cm3 s−1. The equivalent values at 500 K are 2.84, 2.33, 2.93, and 2.33 respectively. This has shown that the greatest change occurs between H and D substitution αe(14/15N2D+)/αe(14/15N2H+) ∼ 0.765/0.857 at 300 K and 0.820/0.795 at 500 K respectively. Values at 500 K are consistently larger than at 300 K. At both temperatures, the rate constants with H substitution are larger than with D substitution for both 14N and 15N. Values with 14N substitution are larger than with 15N for both H and D. At 500 K, the values are independent of whether the ion contains 14N or 15N. Gas-phase 15N fractionation enhancement is predicted in many regions of the interstellar medium including cold and pre-stellar cores. The effect of this fractionation on the recombination process is investigated. The relevance to storage ring measurements of recombination rate constants is considered and applications to the chemistry of the interstellar medium are discussed.Graphical abstractHighlights► The heavier isotopomers of N2H+ recombined slower with electrons. ► This data is compatible with N2D+/N2H+ ratios found in the interstellar medium. ► 15N had lessened, but similar effects on recombination compared to D substitution. ► Isotopic effects on dissociative recombination were compared.

•Experientially measure e-IDR rate constants relevant to Titan.•Establish trends in benzene analogs to aid prediction.•Correlation between e-IDR rate constant and negative Hammett σpara values.•Correlation between temperature dependence and negative Hammett σpara values.An in-depth study of the effects of functional group substitution on benzene’s electron–ion dissociative recombination (e-IDR) rate constant has been conducted. The e-IDR rate constants for benzene, biphenyl, toluene, ethylbenzene, anisole, phenol, and aniline have been measured using a Flowing Afterglow equipped with an electrostatic Langmuir probe (FALP). These measurements have been made over a series of temperatures from 300 to 550 K. A relationship between the Hammett σpara values for each compound and rate constant has indicated a trend in the e-IDR rate constants and possibly in their temperature dependence data. The Hammett σpara value is a method to describe the effect a functional group substituted to a benzene ring has upon the reaction rate constant.