Do Vibrational Excitations of CHD ₃ Preferentially Promote Reactivity Toward the Chlorine Atom?

Abstract

The influence of vibrational excitation on chemical reaction dynamics is well understood in triatomic reactions, but the multiple modes in larger systems complicate efforts toward the validation of a predictive framework. Although recent experiments support selective vibrational enhancements of reactivities, such studies generally do not properly account for the differing amounts of total energy deposited by the excitation of different modes. By precise tuning of translational energies, we measured the relative efficiencies of vibration and translation in promoting the gas-phase reaction of CHD3 with the Cl atom to form HCl and CD3. Unexpectedly, we observed that C-H stretch excitation is no more effective than an equivalent amount of translational energy in raising the overall reaction efficiency; CD3 bend excitation is only slightly more effective. However, vibrational excitation does have a strong impact on product state and angular distributions, with C-H stretch-excited reactants leading to predominantly forward-scattered, vibrationally excited HCl.

Velocity map imaging the dynamics of the reactions of Cl atoms with neopentane and tetramethylsilane

“…[21][22][23][24][25][26][27][28][29][30][31][32] The experimental measurements and dynamical calculations for H-atom abstraction reactions involving simple alkanes illustrate a wealth of dynamical behaviour. For example, the shape of the transition state, with near linear Cl-H-C moiety, is reflected in the low rotational excitation of HCl products; scattering angles are largely determined by impact parameter and their distributions can vary with product rotational and vibrational quantum states; 1 and the reactions of Cl atoms with methane and partially deuterated isotopologues exhibit reagent vibrational mode specificity, [4][5][6][7][9][10][11][12]14,15,[33][34][35][36][37][38][39][40] electronically non-adiabatic pathways, 29,31,41,42 and evidence for scattering resonances. 43 Reactions of functionalized organic molecules (RH = alcohols, 24,44,45 amines, 46 alkyl halides 23,47 and linear and cyclic ethers 24,44,…”

Communication: Imaging the effects of the antisymmetric-stretching excitation in the O(3P) + CH4(v3 = 1) reaction

“…In this regard, the propensity toward translational energy at low collision energies can also be found in many other activated reactions. [29][30][31][35][36][37][38][39][40][41][42][43][44] On intuitive grounds, a finite momentum of the two reactants seems necessary in order to drive reactions over barriers. If correct, a translational propensity in the post-threshold region of activated reactions may well be a general trait; regardless it is an early-, central-, or late-barrier reaction.…”

Communications: A rigorous transition state based approach to state-specific reaction dynamics: Full-dimensional calculations for H+CH4→H2+CH3

“…Considering that the vibrational excitation energies of the 1e, 1a 1 , 2e, and 1e 2 states range between 550 and 1245 cm −1 , 12 the above finding shows that a significant fraction of the vibrational energy of the excited states of CH 4 remains bound in vibrations during the passage of the reaction barrier. Only a part of the 1283 or 1444 cm −1 vibrational energy present in the 1F 2 transferred to the reaction coordinate in the vicinity of the TS and promotes the reaction.…”