IBER 2023

Dynamics of the photodissociation of methylamine: H and CH3 displacement channels

6 Sept 2023, 18:35

1h

Department of Physics, University of Coimbra

Poster Communication Poster Session

Speaker

Prof. Luis Bañares (Universidad Complutense de Madrid)

Description

Due to its similarity with ammonia (NH${}_3$) and because it has been observed in the interstellar medium,[1] methylamine (CH${}_3$NH${}_2$) has received considerable attention in the last decades. The molecular photodissociation of methylamine was studied using the pump-probe method with nanosecond laser pulses. The molecule was excited in the 198 $-$ 203 nm range, and the generated photofragments were detected with the velocity map imaging (VMI) technique, studying the H-atom elimination and the N$-$C bond fission channels separately, combining experiment and theory.
On the one hand, the H-atom displacement channel presents two main dissociation pathways. One is attributed to the formation of CH${}_3$NH($X$) via a conical intersection (CI),[2,3], while the other to CH${}_3$NH($A$), observed for the first time. On the other hand, the recorded images for the NH${}_2$ $+$ CH${}_3$ channel show unstructured Boltzmann-type distributions; however, the speed-dependent anisotropy parameters reveal the presence of two dissociation mechanisms. With a similar landscape of the computed potential energy curves to the N$-$H bond fission, prompt dissociation of the C$-$N bond through the CI is proposed as a minor channel. In contrast, the kinetic energy distribution reflects a major slow dissociation in the ground state, which can arise from frustrated N-H bond cleavage trajectories or vibrationally-hot ground state NH${}_2$ fragments.