The mechanism of H-bond rupture: the vibrational pre-dissociation of C2H2-HCl and C2H2-DCl.
Pair correlated fragment rovibrational distributions are presented following vibrational predissociation of the C2H2-DCl van der Waals dimer initiated by excitation of the asymmetric (asym) C-H stretch. The only observed fragmentation pathways are DCl (v= 0; j= 6-9)+ C2H2(nu2= 1; j= 1-5). These and previously reported data on the related C2H2-HCl species are analysed using the angular momentum (AM) method. Calculations accurately reproduce fragment rovibrational distributions following dissociation of the C2H2-HCl dimer initiated either by excitation of the asym C-H stretch or via the HCl stretch, and those from C2H2-DCl initiated via asym C-H stretch excitation. The calculations demonstrate that the dimer is bent at the moment of dissociation. Several geometries are found that lead to H-bond breakage via a clearly identified set of fragment quantum states. The results suggest a hierarchy in the disposal of excess energy and angular momentum between fragment vibration, rotation and recoil. Deposition of the largest portion of energy into a C2H2 vibrational state sets an upper limit on HCl rotation, which then determines the energy and AM remaining for C2H2 rotation and fragment recoil. Acceptor C2H2 vibrational modes follow a previously noted propensity, implying that the dissociating impulse must be able to induce appropriate nuclear motions both in the acceptor vibration and in rotation of the C2H2 fragment.
Pritchard
Marisian
M
Department of Chemistry, University of Sussex, Brighton, UKBN19QJ.
Parr
Jessica
J
Li
Guosheng
G
Reisler
Hanna
H
McCaffery
Anthony J
AJ
D000114:Acetylene / Q000737:chemistry*; D003903:Deuterium / Q000737:chemistry*; D019281:Dimerization; D006851:Hydrochloric Acid / Q000737:chemistry*; D006860:Hydrogen Bonding; D008956:Models, Chemical; D011789:Quantum Theory; D014732:Vibration
D003903:Deuterium; D000114:Acetylene; D006851:Hydrochloric Acid