Topological effects in low-lying electronic states of linear N₂H₂ ⁺ and HBNH⁺ associated with onset of bending

On the aspect of plane of appearance of Jahn‐Teller and Renner‐Teller intersections in tetra‐atomic system—A case study with HCNO+

“…They demonstrated that, while there has been a regular observation regarding the RT effect, JT‐CI involving the two lowest states (originating from the X 2 Π state on introduction of bending) appear in the molecular plane for HBNH + and out of the plane for N 2 H 2 + . In summary, for states evolved from linear X 2 Π state on introduction of bending, we highlight the following result from the literature: for molecular systems C 2 H 2 + and HBNH + , JT‐CI between the two lowest states evolved and appear in the molecular plane, while for HCNH and N 2 H 2 + , they appear out of the molecular plane. Hence, an argument was made that the symmetric/nonsymmetric nature of the molecules is not related to the issue of plane of appearance of JT‐CI between two states, evolved from X 2 Π state.…”

“…States 1 2 A′ and 1 2 A″ evolve from the linear 1 2 Π state, while states 3 2 A and 4 2 A evolve from the linear 2 2 Π state with the onset of bending. We want to reiterate here that earlier calculations have shown two states evolved from X 2 Π state on introduction of bending and show potential intersections in the molecular plane for C 2 H 2 + and HBNH + and in some nonplanar configurations for N 2 H 2 + and HCNH . In the present section, we want to qualitatively explore what is common in the X 2 Π states of C 2 H 2 + and HBNH + with 1 2 Π state of HCNO + and, similarly, among the X 2 Π states of N 2 H 2 + and HCNH and the 2 2 Π state of HCNO + .…”

“…We have noted, as described in the introduction, while the JT‐CI between the two lowest states of HCNH under such situation appears out of the molecular plane, the JT‐CI between the two lowest states of C 2 H 2 + under a similar situation appears in the molecular plane. Moreover, literature shows that the two lowest states of the pair of molecular systems N 2 H 2 + and HBNH + under a similar situation show a reversal of avenue for potential intersections. In the present article, we want to understand this issue of the plane of appearance of potential intersections.…”

“…In the current article, we report a study on HCNO + , which is similar to the earlier studies in methodology but with an analysis that is distinct in its contribution to the understanding of the issue explained above. The electronic structure of HCNO + is special in that, on introduction of bending, each of the two low‐lying linear X 2 Π states splits into two states.…”

“…We would like to point out that Bene et al tried to justify the specialty of the (1, 2) CI in HCNH by considering the nonsymmetric nature of the molecule in comparison to C 2 H 2 + and commented that more work was needed for a conclusive understanding. Das et al have recently reported different results for similar calculations involving a similar pair of linear molecular systems, N 2 H 2 + and HBNH + . Similar to the pair C 2 H 2 + and HCNH, here, HBNH + has a collinear axis made up of two hetero atoms (B, N), differing in electronegativity in contrast to N 2 H 2 + .…”