Elisabeth A. Wade

Direct measurement of the binding energy of the NO dimer

The binding energy of the NO dimer has been measured directly using velocity-mapped ion imaging. NO dimer is photodissociated to produce NO(X) and NO(A), and the NO(A) is then nonresonantly ionized to NO+. The threshold for production of NO+ ions is measured at 44 893±2 cm−1, which corresponds to a binding energy of 696±4 cm−1.

Differential cross sections for rotational excitation of ND3 by Ne.

We report the first measured differential cross sections for rotationally inelastic collisions between ND(3) and Ne, obtained using velocity-mapped ion imaging. In these experiments, ND(3) molecules initially in the J = 0, K = 0 and J = 1, K = 1 quantum states collide with Ne atoms at a center-of-mass collision energy of 65 meV, leading to rotational excitation of ND(3). Differential cross sections are then determined from images of the rotationally excited scattered molecules using an iterative extraction method. These measurements complement and compare well with previous measurements of differential cross sections for the ammonia-rare gas system (Meyer, H. J. Chem. Phys. 1994, 101, 6697.; Meyer, H. J. Phys. Chem. 1995, 99, 1101.) and are also relevant to the production of cold ND(3) molecules by crossed-beam scattering (Kay, J. J.; van de Meerakker, S. Y. T.; Strecker, K. E.; Chandler, D. W. Faraday Discuss. 2009, DOI: 10.1039/B819256C).

Photochemistry of chloropicrin in cryogenic matrices

Abstract The photolysis of chloropicrin (CCl3NO2) was investigated in Ar and N2 cryogenic matrices. The extent of reaction was monitored using FT-IR spectroscopy. Phosgene and nitrosyl chloride were the observed photoproducts at all wavelengths investigated (220, 251, 313, 365, and 405 nm). When the photolysis was performed with 220, 251, or 313 nm light, two additional bands were also observed. These bands have been assigned to CCl3ONO. Chloropicrin was also photolyzed in the presence of O2 and 18 O 2 . 18 O -labeled photoproducts were not detected in cryogenic matrices.

Infrared Emission Following Photolysis of Methylisothiocyanate and Methylthiocyanate

Methylisothiocyanate (CH(3)NCS) was photolyzed at 193 and 248 nm, and the resulting time-resolved infrared emission was observed. Similar experiments were performed on methylthiocyanate (CH(3)SCN) photolyzed at 193 nm. Previous work suggested that these isomers undergo excited-state isomerization prior to dissociation, but other experiments have contradicted this claim. In the infrared emission experiments, we observed the same products from both starting materials, supporting the theory of excited-state isomerization prior to dissociation. Methylisothiocyanate is the active ingredient in a widely used pesticide and has been observed to form highly toxic methyl isocyanate (CH(3)NCO) under environmental conditions. The mechanism for this formation has been unclear, but must involve some oxygen-containing species. At 248 nm, methylisothiocyanate was photolyzed alone and with three atmospheric oxidizers: O(2), NO, and NO(2). No chemical reaction was observed with O(2), whereas secondary reactions were observed with NO and NO(2). When methylisothiocyanate was photolyzed with NO(2), methyl isocyanate (CH(3)NCO) was observed, suggesting a likely environmental mechanism for methyl isocyanate formation.