Reaction potential surface for B+(1S) + H2 ⇒ HBH+(1gg+), BH+(2∑) + H(2S)

Jeff Nichols, Maciej Gutowski, Samuel J. Cole, Jack Simons

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

The reaction of B+(1S) with H2 on the ground potential energy surface is examined using ab initio electronic structure methods. In the entrance channel, a weakly bound T-shaped B+⋯H2 complex of C symmetry is found to lie 422 cm-1 below the B+ + H2 reactant energy. Its H-H internuclear distance is only slightly distorted from that of H2; the B-H distance (ca. 2.6 A) is much longer than the covalent bond length in BH+ (1.2 Å). Further along the reaction coordinate is found a narrow valley characterized by strong B+-to-H2 interreactant forces but very small distortion of the H-H bond length or the H-H vibrational frequency. Further up the floor of this valley, a geometry is reached at which, through second-order Jahn-Teller coupling, the asymmetric motion (of b2 symmetry) develops negative curvature and thus becomes geometrically unstable. From this point of instability, distortion along the asymmetric mode can lead directly to the BH+(2∑) + H products. The energy of this instability point is 22 842 cm-1 above B+ + H2 and 2021 cm-1 or ca. 0.25 eV above the thermodynamic reaction threshold for BH+ + H formation, which is predicted to be 20 000 cm-1. In addition, a geometrically stable linear HBH+(1g+) species is found to lie 14712 cm-1 below B+ + H2. Its BH bond length (rBH = 1.187 Å) is only slightly shorter than that in BH+ (1.199 Å). All of these findings are in reasonable agreement with known experimental data on the reactivity of B+ with H2. However, another (collinear) reaction path has been found that leads to BH+(2∑) + H without any barrier above the thermodynamic requirement; this path, if operative, is not consistent with experimental findings. A proposal is offered to explain how the path that passes through the point of instability may be of more relevance to the guided-ion beam data than the lower energy collinear path.

Original languageEnglish
Pages (from-to)644-650
Number of pages7
JournalJournal of Physical Chemistry
Volume96
Issue number2
DOIs
StatePublished - 1992
Externally publishedYes

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