Are linear molecules really linear? I. Theoretical predictions

Hirano, Tsuneo

Permalink

https://hdl.handle.net/2142/100723 Copy

Description

Title

Are linear molecules really linear? I. Theoretical predictions

Author(s)

Hirano, Tsuneo

Contributor(s)

• Jensen, Per
• Nagashima, Umpei

Issue Date

2018-06-19

Keyword(s)

Mini-symposium: New Ways of Understanding Molecular Spectra

Abstract

In spectroscopic parlance, a linear triatomic molecule is one whose potential energy minimum occurs at a linear geometry. We have recently discusseda,b,c that any linear triatomic molecule will be observed as being “bent” on ro-vibronic average in any ro-vibronic state. As quantum mechanics asserts, we have to characterize Nature through “observation.” Theoretically we make observations of molecular structures by calculating the expectation values of the structural parameters over the relevant ro-vibronic wavefunctions. In computational molecular spectroscopy studies, we have shown that for many linear triatomic molecules such as 6∆ FeNC, 6∆ FeCN, 2Π BrCN+, 3Φ CoCN, 2∆ NiCN, 1Σ + CsOH, 3Σ − FeCO, and 2Π NCS, the ro-vibrationally averaged structure (zero-point structure, for example) is slightly bent with a bond angle supplement 180◦ − 6 (A-B-C) [where 6 (AB-C) is the bond angle] in the range from 7.5◦ (NCS) to 22.5◦ (C3). We have also described the theoretical backgroundb for this fact using a Laguerre-Gauss type wavefunction for the doubly degenerate bending oscillator; the average “bentness” is basically caused by the inseparability of the bending motion from the free rotation about the molecular axis. Our finding is in contradiction to the well-established paradigm in spectroscopy that the ro-vibrationally averaged structure of a linear molecule is linear. In particular, it throws doubt on the so-called r0 structures routinely determined for linear triatomic molecules under the a priori assumption that ro-vibrationally averaged bond-angle of a linear molecule should be 180◦. In the following talk, we discuss how experimentally derived rotational-constant values are to be interpreted.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/100723

DOI

10.15278/isms.2018.TB02

Copyright and License Information

Copyright 2018 Tsuneo Hirano

Owning Collections