Complete and detailed experimental transition probability density functions P(E′,E) have been determined for the first time for collisions between a large, highly vibrationally excited molecule, toluene, and several bath gases. This was achieved by applying the method of kinetically controlled selective ionization (KCSI) (Paper I [J. Chem. Phys. 112, 4076 (2000), preceding article]). An optimum P(E′,E) representation is recommended (monoexponential with a parametric exponent in the argument) which uses only three parameters and features a smooth behavior of all parameters for the entire set of bath gases. In helium, argon, and CO2 the P(E′,E) show relatively increased amplitudes in the wings—large energy gaps |E′−E|—which can also be represented by a biexponential form. The fractional contribution of the second exponent in these biexponentials, which is directly related to the fraction of the so-called “supercollisions,” is found to be very small (<0.1%). For larger colliders the second term disappears completely and the wings of P(E′,E) have an even smaller amplitude than that provided by a monoexponential form. At such low levels, the second exponent is therefore of practically no relevance for the overall energy relaxation rate. All optimized P(E′,E) representations show a marked linear energetic dependence of the (weak) collision parameter α1(E), which also results in an (approximately) linear dependence of 〈ΔE〉 and of the square root of 〈ΔE2〉. The energy transfer parameters presented in this study form a new benchmark class in certainty and accuracy, e.g., with only 2%–7% uncertainty for our 〈ΔE〉 data below 25 000 cm−1. They should also form a reliable testground for future trajectory calculations and theories describing collisional energy transfer of polyatomic molecules.

Collisional energy transfer probabilities of highly excited molecules from kinetically controlled selective ionization (KCSI). II. The collisional relaxation of toluene: P(E ′ ,E) and moments of energy transfer for energies up to 50 000 cm−1 State-resolved collisional energy transfer in highly excited NO 2 . I. Cross sections and propensities for J, K, and m J changing collisionsThe coupled channel density matrix method for open quantum systems: Formulation and application to the vibrational relaxation of molecules scattering from nonrigid surfaces

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Full sets of experimentally determined "collisional energy transfer probability distributions", P(E', E ) , have become available first time for the deactivation of highly vibrationally excited large molecules. These data from KCSI measurements (kinetically controlled selective ionization) on the vibrational relaxation of toluene ((E,) = SOWcm-') and azulene ((E,,) = 30000 and 20000cm-') are discussed with emphasis on systematic aspects. Under proper conditions the KCSI measurements become self-calibrating. This provides i.a. very high quality results on ( A E ) , free from possible calibration errors. Detailed second moments are given and consequences on energy distributions during relaxation are discussed. The P(E',E) distributions show extended wings Of finite probabilities for transfer of large AE. Their relative role is characterized. A double-exponential representation of P(E',E) is useful, mainly for atomic and shall molecular collider gases. However, a more universal and better analytical representation of P(E', E ) , using one parameter less, is recommended. The fraction of "supercollisions" (independent from details of definition) is very small.

The properties of several cinnamic acid compounds used as matrices for matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) were investigated as standard dried droplet (DD) and vacuum sublimed preparations. The differences between both preparation methods were analyzed with regard to matrix grain size, internal ion energy, initial velocity, analyte intensity, and analyte incorporation depth. Some of the used cinnamic acid derivatives exhibit clearly reduced grain sizes as sublimed preparations compared with standard DD approaches. In these cases higher effective temperatures could be measured accompanied by increased analyte intensities, which can be explained by stronger volatilization processes caused by a hindered heat dissipation resulting in a raised analyte transfer into the gas phase. For all sublimed compounds, a strong increase of the initial ion velocity compared with DD preparations could be measured. Higher initial ion velocities correlate with a decrease in internal ion energy which might be attributed to the very uniform crystal morphology exhibited by sublimed compounds. For sublimed matrices without reduced grain size, at least slightly higher analyte intensities could be detected at raised laser fluences. Analyte accumulation in the uppermost matrix layers or the detected higher ion stability can be explanations for these results. Ever increasing numbers of samples call for automation in high-throughput workflows. One of the key areas for progress in automated MALDI analyses consists of improved sample preparation techniques. Numerous efforts have been conducted for improving the preparation step, e.g., the generation of thin uniform matrix layers with high shot-to-shot reproducibility using the aerospray technique by combination of matrix and nitrocellulose [4] or for analysis of synthetic polymers [5]. Also, electrospray deposition and vacuum deposition were reported to yield homogeneous sample preparations with increased analyte intensities [6 -9]. Matrix deposition by sublimation for MALDI imaging has been reported to yield more intense signals with less alkali adducts compared with the electrospray technique [10]. Additionally, sublimed matrix spots deposited on extremely hydrophobic surfaces described in [11][12][13][14] offer a variety of beneficial properties compared with standard dried droplet (DD) preparations: The main advantage of sublimed matrix spots compared with standard DD preparations are higher analyte sensitivities [14 -17]. This is likely related to the formation of considerably smaller crystals and narrow size distribution of thin-film sublimed matrices, such as ␣-cyano-4-hydroxycinnamic acid (CHCA), compared with DD preparations with comparatively large particle sizes and broader size distribution [15]. As a consequence of this, the specific matrix surface area as well as the amount of potential binding places increases compared with standard DD precipitates, which will result in increased analyte binding properties. Additionally, th...