Jonathan J. Schroden

Dynamics of CO elimination from reactions of yttrium atoms with formaldehyde, acetaldehyde, and acetone

Reactions of neutral, ground-state yttrium atoms with formaldehyde, acetaldehyde, and acetone (Y+RR′CO, where R,R′=H,CH3) were studied in crossed molecular beams. At collision energies greater than 24 kcal/mol, four product channels were observed corresponding to elimination of CO, H2, H, and nonreactive scattering. For the dominant CO elimination channel, a large fraction (34%–41%) of the available energy appeared as kinetic energy of the products. RRKM modeling indicated this was a result of two factors: a large potential energy barrier for R′ migration leading to (R)(R′)YCO and dissociation of this complex prior to complete energy randomization. The CM angular distributions were all forward–backward symmetric, indicating the existence of at least one long-lived reaction intermediate. The angular distributions ranged from being quite forward–backward peaking for the Y+H2CO reaction to isotropic for Y+(CH3)2CO. A simple equation is derived based on statistical complex theory that relates the shape of the...

C-C versus C-H Bond Activation of Alkynes by Early Second-Row Transition Metal Atoms

The reactions of Y (a2D), Zr (a3F), Nb (a6D), Mo (a7S), and electronically excited-state Mo* (a5S) with propyne (methylacetylene) and 2-butyne (1,2-dimethylacetylene) were investigated using crossed molecular beams. For all of the metals studied, reactions with propyne led to H2 elimination, forming MC3H2. For Y + propyne, C-C bond cleavage forming YCCH + CH3 also was observed, with an energetic threshold in good agreement with an earlier determination of D0(Y-CCH). For Y + 2-butyne, three reactive channels were observed: YC4H4 + H2, YC3H3 + CH3, and YC3H2 + CH4. The C-C bond cleavage products accounted for 21 and 27% of the total products at Ecoll = 69 and 116 kJ/mol, respectively. For Zr and Nb reactions with 2-butyne, competition between H2 and CH4 elimination was observed, with C-C bond cleavage accounting for 12 and 4% of the total product signal at Ecoll = 71 kJ/mol, respectively. For reactions of Mo and Mo* with 2-butyne, only H2 elimination was observed. The similarity between reactions involving two isomeric species, propyne and allene, suggests that H atom migration is facile in these systems.

Crossed beams studies of Mo(a 7S3) and Mo*(a 5S2) collisions with CH4 and C2H6

The interactions of Mo(a 7S3) and Mo*(a 5S2) with methane, CH4, and ethane, C2H6, were studied under single collision conditions using the crossed molecular beams technique. Ground state Mo(a 7S3) atoms were found to be unreactive at all collision energies studied up to 〈Ecoll〉=35.4 kcal/mol. Nonreactive scattering of Mo(a 7S3) with methane and ethane was studied and compared to collisions with Ne and Ar. A forward peaking center-of-mass angular distribution, T(Θ), was necessary to simulate the elastic collisions with inert gases as well as inelastic collisions with the alkanes. At a collision energy of 14.4 kcal/mol with CH4 and 21.0 kcal/mol with C2H6, inelastic collisions were found to transfer ∼10% and ∼19% of the initial kinetic energy into alkane internal energy, respectively. For collisions of Mo*(a 5S2)+CH4, the dehydrogenation product, MoCH2, was observed at all collision energies studied down to 2.1 kcal/mol. The reaction Mo*(a 5S2)+C2H6→MoC2H4+H2 was observed down to 〈Ecoll〉=4.5 kcal/mol. For a...

Dynamics of Y+H2CO reactions

The reactions of ground state yttrium atoms (Y) with formaldehyde (H2CO) have been studied in crossed molecular beams as a function of collision energy (Ecoll). The potential energy barrier for C–H insertion is found to lie below 12 kcal/mol. It is proposed that the reaction is initiated by C–H insertion, producing HYCHO followed by H atom migration forming H2YCO. Although Y–CO bond fission leading to YH2+CO is dominant, a secondary minor channel also leads to the production of YCO+H2. Formation of YCHO+H is not observed at 16 kcal/mol, but is clearly seen at 31 kcal/mol, indicating that D0(Y–CHO) lies between 58 and 73 kcal/mol.

Reactions of Neutral Gas-Phase Yttrium Atoms with Two Cyclohexadiene Isomers

The reactions of neutral ground-state yttrium (Y) atoms with 1,3- and 1,4-cyclohexadiene (CHD) were studied using crossed molecular beams. Formation of YC(6)H(6) + H(2) and YH(2) + C(6)H(6) was observed for both isomers at collision energies (E(coll)) of 31.3 and 13.0 kcal/mol. Measured product branching ratios at E(coll) = 31.3 kcal/mol indicated that YH(2) + C(6)H(6) was the dominant channel, accounting for >97% of the products. An additional minor product channel, YC(4)H(4) + C(2)H(4), was observed for 1,3-CHD at the higher E(coll). The reaction threshold for YC(4)H(4) formation was determined to be 29.5 ± 2.0 kcal/mol based on fits to the data.