Roaming signature in photodissociation of carbonyl compounds

Photodissociation Dynamics of CO-Forming Channels on the Ground-State Surface of Methyl Formate at 248 nm: Direct Dynamics Study and Assessment of Generalized Multicenter Impulsive Models

“…The features of the roaming saddle point and the related intrinsic reaction coordinate of methyl formate are quite similar to those found in aldehydes. ,,− ,,,,− The C···OCH 3 bond length increases until reaching a distance larger than 2.5 Å, where the HCO moiety rotates along its CO axis and transfers the H atom to OCH 3 . It is well-known that the roaming mechanism can only produce CO with a very low energy.…”

“…Inspired by experimental studies carried out in these last few years on the photodissociation of methyl formate, − ,, we performed an investigation on the dynamics of the photoinitiated processes, with a wavelength of 248 nm, which characterizes this ester, aimed at providing tools to identify the various channels in the ground state S 0 with the production of CO. Dynamics simulations are based on the assumptions of the RRKM theory and the minimum energy path and are initiated from the saddle points of the investigated dissociation pathways. We have examined five channels characterized by different energy distributions: four of them with methanol + CO as products including a pathway characterized by the roaming saddle point and a fifth channel that produces H 2 + CO + H 2 CO. We have also analyzed and compared the results of the present work with those obtained from velocity map imaging ,, and FTIR experiments. − , The results show that initiating the direct dynamics from the saddle points, none of the CO-forming pathways can provide satisfactory explanations to all of the experimental evidence.…”

“…To distinguish the product of RTS from other methanol-forming channels, the detection of vibrational excitation in methanol might not be a proper choice. Indeed, the dynamical signature of the roaming mechanism in the CO-forming channel of carbonyl compounds is the bond-selective vibrational excitation of the coproduct. , However, it might be hard to provide a quantitative determination of the vibrational energy of polyatomic products from their infrared emission spectra. For example, the mean values of vibrational energy distribution in methanol products from TS1, TS4, TS5, and RTS are about 56, 39, 56, and 90 kcal/mol, respectively, after subtracting the zero-point energy (∼32 kcal/mol).…”

“…Classical trajectories permitted one to assign to the first case a mechanism that involved the minimum energy path and in the second case the formation of a weakly linked complex, with hydrogen abstraction, namely, roaming. The roaming mechanism in unimolecular dissociation was later found in aldehydes, − acetone, , nitrate radical, − alkane, methylnitrite, , and other molecules, − as well as different physical interpretations to roaming mechanism, − both can be found in several review papers. ,,,,,, Roaming was then found in methyl formate HC­(O)­OCH 3 , the simplest of esters . This molecule, initially studied in combustion chemistry, has also attracted the interest of astrochemists (see for example refs and ).…”

Pattern analysis of the impact‐parameter dependent trajectories for the H + H2 exchange reaction at T = 3 and 300 K: A characteristic propensity for reactive versus nonreactive trajectories found in the time‐dependent interaction potential and a roaming‐like libration motion at cold temperature

“…[36] Reaction pathways, which bypass the TSs, such as roaming pathways are discussed in the previous studies. [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] We learned that the classical trajectory calculations serve us the detailed reaction dynamics. [20][21][22][23][24][25][26][27]49] The Polanyi rule is a notable example of the usefulness of the trajectory calculation in which how the location of the energy barrier along the reaction coordinate determines chemical reaction dynamics.…”