Apart from particle size distribution, spray velocity is one of the most important aerosol characteristics that influence lung deposition of inhaled drugs. The time period over which the aerosol is released (spray duration) is also important for coordination of inhalation. Respimat Soft Mist Inhaler (SMI) is a new generation, propellant-free inhaler that delivers drug to the lung much more efficiently than pressurised metered dose inhalers (pMDIs). The objective of this study was to compare the velocity and spray duration of aerosol clouds produced by Respimat SMI with those from a variety of chlorofluorocarbon (CFC) and hydrofluoroalkane (HFA) pMDIs. All inhalers contained solutions or suspensions of bronchodilators. A videorecording method was used to determine the aerosol velocity. For spray duration, the time for generation of the Soft Mist by Respimat SMI was initially determined using three different methods (videorecording [techniques A and B], laser light diffraction and rotating disc). Videorecording was then used to compare the spray duration of Respimat SMI with those from the other inhalers. The Soft Mist produced by Respimat SMI moved much more slowly and had a more prolonged duration than aerosol clouds from pMDIs (mean velocity at a 10-cm distance from the nozzle: Respimat SMI, 0.8 m/sec; pMDIs, 2.0-8.4 m/sec; mean duration: Respimat SMI, 1.5 sec; pMDIs, 0.15-0.36 sec). These characteristics should result in improved lung and reduced oropharyngeal deposition, and are likely to simplify coordination of inhaler actuation and inhalation compared with pMDIs.

Vibrational overtone excitation of HCN in the wavelength region 6 500 cm−1–18 000 cm−1 is used to initiate the endothermic reaction of chlorine and hydrogen atoms with HCN. HCN is excited to the overtone levels (002), (004), (302), (105), and (1115). The labeling of the vibrational levels (ν1ν2l2ν3) corresponds to the normal modes ν1=CN, ν2=bend, ν3=CH, and l2=vibrational angular momentum. The product state distribution of CN(X 2Σ+) is completely analyzed by laser induced fluorescence (LIF). Excitation of the first overtone of CH-stretch leads to vibrationally excited CN in the reaction of Cl+HCN(002), implying the existence of a long living complex. The CN vibrational excitation increases with increasing H–CN stretch excitation. However, a slightly higher CN vibrational excitation is found when at the same internal energy of HCN three quanta of CN-stretch and two quanta of CH-stretch are excited. Therefore, the energy is not completely redistributed in the collision complex. The ratio of rate constants between the reactions of HCN(004) and HCN(302) with Cl is 2.8±0.6. The CN product vibrational excitation decreases again, when HCN is excited to the (105) state. At these high HCN vibrational energies the reaction mechanism seems to change toward a more direct reaction where the time left is not sufficient for energy randomization. The reaction of hydrogen with HCN(004) leads to CN-products with a similar vibrational distribution, as in the case of chlorine, but with a lower rotational excitation. The reaction H+HCN(302) shows no significant generation of CN products and a lower limit of the ratio of rate constants, k(004)/k(302)≳4, is obtained.

The influence of rotation and vibration on the reactivity and the dynamics of the reaction X+HCN(ν1,ν2,ν3,J)→HX+CN(v,J) with X=H, Cl has been studied. The HCN molecule is prepared in a specific rovibrational level by IR/VIS overtone excitation in the wavelength region 6500–18 000 cm−1. The H atoms are generated by laser photolysis of CH3SH at 266 nm, the Cl atoms are formed in the photodissociation of Cl2 at 355 nm. The CN products are probed quantum state specifically by laser-induced fluorescence (LIF). For low rotational states of HCN, the reactivity of Cl and H is independent of the initial rotational state. However, an enhancement in reactivity of the Cl+HCN reaction is observed when the time of rotation becomes comparable to the passing time of the Cl atom. The reaction of Cl as well as of the H atom with HCN shows strong mode specific behavior, implying a simple direct reaction mechanism, which is also supported from Rice–Ramsperger–Kassel–Marcus (RRKM) calculations. An increase in CH stretch vibration increases both the reaction rate and the CN product vibration. Channeling energy in CN stretch vibration has only a minor effect on the reactivity and the CN product vibration even decreases. Trajectory calculations of the H+HCN system agree with the experimental results. The dependence of reaction rates on reactant approach geometry is investigated by preparing aligned reactants using linear polarized light. The CN signal is markedly influenced by the prepared alignments (steric effect). The experimental results suggest that the reaction of hydrogen and chlorine atoms with vibrationally excited HCN proceeds mainly via a collinear transition state, but the cone of acceptance is larger for chlorine atoms.

The quantum state resolved reaction dynamics of HCN(0 00 v3) with O(1D) atoms were investigated by analyzing the complete product state distributions of OH(X 2ΠΩ,v,J) and CN(X 2Σ+,v,J) using laser induced fluorescence (LIF). The influence of the CH-stretching mode on the reaction dynamics and different branching ratios was inspected by exciting HCN to its first overtone band of the ν3 CH stretch in the 1.5 μm region. The oxygen atom in the 1D state was generated in a laser photolysis of ozone at a wavelength of 266 nm. The measured rotational and vibrational distributions of the products were compared with statistical results from phase space theory (PST). Nearly statistical rotational and vibrational distributions are obtained for CN(X 2Σ+) in v=0–3. The rotational and vibrational distributions of OH(X 2ΠΩ) are colder than statistically expected. Insertion of O into the CN bond with subsequent hydrogen migration seems to be a better characterization of the the reaction mechanism than an insertion of the oxygen atom into the CH bond. Direct abstraction of hydrogen to form OH is improbable to describe the molecular process.

The photodissociation of jet-cooled OClO following excitation into the Ã 2A2 state at around 350 nm was investigated in homogeneous OClO and large heterogeneous Ar/OClO and H2O/OClO clusters (estimated cluster size n̄∼800–2600) by probing the O (3P) and ClO (X̃ 2Π) photofragments using the resonance enhanced multiphoton ionization-time of flight technique. Action spectra, photofragment excitation spectra and photofragment speed distributions were recorded and compared to those for monomer dissociation. OClO was found to occupy both surface and interior sites in the heterogeneous clusters with the percentage of surface and interior dissociation processes being ∼50% for large cluster sizes. Both O and ClO photofragments generated in the cluster interior are translationally thermalized with T∼300 K and the ClO fragments are strongly rotationally and vibrationally relaxed. This is most important for vibration as monomer dissociation yields ClO containing up to 8 vibrational quanta at this photolysis wavelength. Photodissociation on the cluster surface is found to proceed with little interaction with the cluster host. The distribution of counterfragment masses leads to a broadening of the speed distributions compared with monomer dissociation. In addition, cluster chemistry was found to occur in OClO-rich heterogeneous clusters as manifested by detection of O photofragments with velocities exceeding the highest thermodynamically possible value. This result, consistent with that from homogeneous OClO cluster dissociation, indicates the presence of small OClO aggregates on the surface and within heterogeneous clusters. From a standpoint of atmospheric chemistry, H2O/OClO clusters yield a substantial fraction of thermalized primary photofragments, in contrast to OClO monomer dissociation.