Proton transfer reactions of H+(H2O)n=2–11 with methanol, ammonia, pyridine, acetonitrile, and acetone

Abstract

We report here the first measurements of rate constants involving cluster ions with more than five ligands. We have measured rate constants, or lower limits to rate constants, for the reactions of H+(H2O)n=2–11 with NH3, CH3CN, CH3OH, CH3COCH3, and C5H5N (pyridine). The experimental techniques needed to study these ions and neutrals at low temperatures are described. The reactions all proceed rapidly by proton transfer with varying degrees of ligand transfer. At low temperatures the rate constants are larger than the collision rate constant based on an ion–dipole potential. Reasons for this are examined. Thermal dissociation appears to control the size distribution of the primary ion clusters and to affect the observed product distribution.

Detection of RO2 radicals and other products from cyclohexene ozonolysis with NH4+ and acetate chemical ionization mass spectrometry

“…Duty cycle corrected counts per second (dcps, normalized to m/ z = 101; are used in order to compensate for the mass-dependent transmission of the TOF mass spectrometer ( (Breitenlechner et al, 2017). For 3-hexanone and heptanone we obtained a sensitivity of 28 dcps/pptv, which is in agreement with the calculated sensitivity taking into account the duty cycle corrected NH 4 + X n adduct ion count rates, the pressure and the reaction time in the reaction chamber (80 mbar; 4 ms) and using 2-3 x 10 −9 cm 3 s −1 as a fast ligand switching reaction rate constant close to the collisional limit value (Viggiano et al, 1989). Consequently, only lower end product concentrations can be given using a sensitivity of 28 dcps/pptv.…”

Methyl cyanide and hydrogen cyanide measurements in the lower stratosphere: Implications for methyl cyanide sources and sinks

“…The aircraft-based IMRMS instrument used for the present measurements has been described previously [Arnold and Hauck, 1985 whose measured rate coefficient is k 2 = 3.06(300/T)x 10 '9 cm 3 s -1 which is nearly equal to the calculated collision rate coefficient [Viggiano et al, 1988]. The uncertainty of k2 is also +30%.…”

Acetone and acetonitrile in the tropical Indian Ocean boundary layer and free troposphere: Aircraft‐based intercomparison of AP‐CIMS and PTR‐MS measurements

“…The reaction efficiency is decreasing with an increasing number n of water ligands. Depending on the number of water ligands, also a backward reaction is possible [Viggiano et al, 1988]. Therefore the detection sensitivity of acetone and acetonitrile is dependent on the water vapor concentration in the API.…”