Vibrational relaxation of NO+ (v) ions in neutral collisions

Near-resonant vibration-to-vibration energy transfer in the NO+-N2 collisions

First principles model calculations of the vibration-to-vibration (VV) energy transfer (ET) processes NO(+)(nu=1)+N(2)(nu=n-1)-->NO(+)(nu=0)+N(2)(nu=n)+(28.64n-14.67) cm(-1) and NO(+)(nu=n)+N(2)(nu=0)-->NO(+)(nu=n-1)+N(2)(nu=1)+(32.52(n-1)+13.97) cm(-1) for n=1-3 in the 300-1000 K temperature range are performed. The VV ET probability is computed for three mechanisms: (1) The charge on NO(+) acting on the average polarizability of N(2) induces a dipole moment in N(2) which then interacts with the permanent dipole moment of NO(+) to mediate the energy transfer. (2) The charge on NO(+) acting on the anisotropic polarizability of N(2) induces a dipole moment in N(2) which then interacts with the permanent dipole moment of NO(+) to mediate the energy transfer. (3) The dipole moment of NO(+) interacts with the quadrupole moment of N(2) to mediate the energy transfer. Because the probability amplitudes of the second and third mechanisms add coherently the ET probability for these two mechanisms is given as a single number. The probability of energy transfer per collision is in the 5 x 10(-3) range. The results of this calculation are compared with the available experimental data. This calculation should help quantify the role of NO(+) in the energy budget of the upper atmosphere.

Analysis of petrol and diesel vapour and vehicle engine exhaust gases using selected ion flow tube mass spectrometry

We have used selected ion flow tube mass spectrometry (SIFT-MS) to analyse the vapours emitted by petrol and diesel fuels and the exhaust gases from petrol (spark ignition) and diesel (compression ignition) engine vehicles fitted with catalytic converters. Only those components of these media that have significant vapour pressures at ambient temperatures were analysed and thus particulates were obviously not detected. These media have been analysed using the full scope of SIFT-MS, i.e., with the three available precursor ions H3O+, NO+ and O2+. The combination of the H3O+ and NO+ analyses is seen to be essential to distinguish between different product ions at the same mass-to-charge ratio (m/z) especially in identifying aldehydes in the exhaust gases. The O2+ precursor ions are used to detect and quantify the large amount of nitric oxide present in the exhaust gases from both engine types. The petrol and diesel vapours consist almost exclusively of aliphatic alkanes, alkenes and alkynes (and dienes) and aromatic hydrocarbons. Some of these compounds appear in the exhaust gases together with several aldehydes, viz. formaldehyde, acetaldehyde, pentanal, pentenal (acrolein), butenal, and also methanol and ethanol. Acetone, nitric oxide and ammonia are also present, acetone and nitric oxide being much more abundant in the diesel exhaust gas than in the petrol exhaust gas. These data were obtained from samples collected into pre-evacuated stainless steel vessels. Trapping of the volatile compounds from the gas samples is not required and analysis was completed a few minutes later. All the above compounds are detected simultaneously, which demonstrates the value of SIFT-MS in this area of research.

A Personal history of the early development of the flowing afterglow technique for ion-molecule reaction studies

A personal perspective of the historical development of the flowing afterglow (FA) technique for measuring thermal energy ion-molecule reaction rate constants is presented. The technique was developed in the period starting in late 1962 in what was then the National Bureau of Standards in Boulder, Colorado. The motivation was primarily to obtain a quantitative understanding of the ion chemistry of the terrestrial ionosphere, a program that was substantially achieved. The thermal energy measurements were extended in temperature from 300 K to a range of 80 K-900 K and subsequently to a center-of-mass kinetic energy range up to ∼ 2 eV with the introduction of a drift tube into the FA.The chemical versatility, in regard to both the ion and the neutral reactants measured, remains unequaled and FA systems are currently in widespread use around the world for a variety of chemical research programs.