No abstract

This article presents and overviews the CHIMERA program package, which provides a user-friendly graphical interface between quantum chemistry and chemical kinetics programs. CHIMERA facilitates calculations of rate constants for gas-phase reactions using transition state and Rice-Ramsperger-Kassel-Marcus theories. The program includes computational modules for simulation of gas-phase kinetics using simplified reactor models and for computation of chemical equilibria. The review includes a description of the theory implemented in the code, the program description, the general strategy of calculations using CHIMERA, and illustrative examples of the program application.

A field-deployable quadrupole ion-trap mass spectrometer with an atmospheric pressure interface is designed, built, and characterized. The instrument enclosure (48 cm × 43 cm × 42 cm) includes a roughing pump and a helium lecture bottle; the total weight of the instrument is 68 kg. Peak power consumption during the instrument operation is ∼500 W. The instrument has a mass range of m/z 30-2500, across which it provides better than unit mass resolution. The typical peak width at half height is 0.3 Th for a scan speed of 4000 Th/s. Operation of the instrument with electrospray and atmospheric-pressure matrix-assisted laser desorption ionization (AP-MALDI) ion sources is demonstrated. AP-MALDI analysis of low femtomole amounts of peptides reveals that the sensitivity of the instrument is on par with modern commercially available quadrupole ion-trap mass spectrometers. Tandem mass spectrometry capabilities of the instrument include simultaneous isolation and fragmentation of several different compounds. Two ways to reduce the size, weight, and power consumption of the portable instrument were explored, and results of these initial studies are presented. One of the ways includes utilization of hydrogen as a buffer gas for operation of the ion-trap mass analyzer in combination with a metal hydride method for storage of hydrogen in a compact rechargeable cartridge. Furthermore, careful selection of the inlet capillary dimensions allowed to eliminate the first "1 Torr" stage of the differential pumping without any significant loss of the instrument sensitivity. The elimination of this first pumping stage removed two turbo drag pumps, which substantially decreased the instrument's maximum power consumption (to ∼300 W in peak use, and ∼150 W during standby), as well as its size (to 30 cm × 43 cm × 50 cm) and weight (to 35 kg).

Thermodynamic equilibrium and kinetics of the gas-phase reaction between TiCl 4 and NH 3 have been studied computationally using results from recent quantum mechanical calculations of titanium tetrachloride ammonolysis.1 These calculations were based upon the transition state theory for the direct reactions and RRKM theory for the reactions proceeding via intermediate complex. Rate constants for the barrierless reactions were expressed through the thermodynamic characteristics of the reagents and products using a semiempirical variational method. The kinetic simulation of the gas-phase steps of CVD was performed within a model of a well-stirred reactor at temperatures 300-1200 K and residence times between 0.1-2 s. At temperatures below 450 K formation of donor-acceptor complexes between TiCl 4 and NH 3 is the dominating process. At higher temperatures sequential direct ammonolysis takes place. At typical LPCVD conditions the only product of the first step of ammonolysis, TiCl 3 NH 2 , is formed in substantial amount.

A new Fourier transform ion cyclotron resonance mass spectrometer based on a permanent magnet with an atmospheric pressure ionization source was designed and constructed. A mass resolving power (full-width-at-half-maximum) of up to 80,000 in the electron ionization mode and 25,000 in the electrospray mode was obtained. Also, a mass measurement accuracy at low-ppm level has been demonstrated for peptide mixtures in a mass range of up to 1200 m/z in the isotopically resolved mass spectra. (J Am Soc Mass Spectrom 2007, 18, 1552-1558