Higher order PT terms in molecular parameters

In summary, textbooks on molecular spectroscopy, such as Molecular Spectroscopy by J. Demaison and the Handbook of Molecular Constants by A.J. Merer, contain information on higher order terms of molecular parameters, including the spin rotational parameter ##\gamma##. These sources provide tables and equations up to fourth order for spin-rotation constants.
  • #1
BillKet
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Hello! Is there a place where I can find the expressions for higher order terms of molecular parameters (in particular the spin rotational parameter, ##\gamma##)? All the papers I find just show them up to second order. Thank you!
 
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  • #2
You can find the expressions for higher order terms of molecular parameters in various textbooks on molecular spectroscopy. A good starting point is the book Molecular Spectroscopy by J. Demaison, which contains a chapter on spin-rotation constants and their higher order terms. You can also find useful information in the Handbook of Molecular Constants by A.J. Merer, which includes tables of spin-rotation constants up to fourth order.
 

Related to Higher order PT terms in molecular parameters

1. What are higher order PT terms in molecular parameters?

Higher order PT terms in molecular parameters refer to the contributions from higher order derivatives of the potential energy surface (PES) in the calculation of molecular properties. These terms are usually neglected in traditional quantum chemical calculations due to their relatively small contributions, but can become important for highly accurate calculations or for systems with strong anharmonicities.

2. How do higher order PT terms affect molecular properties?

The inclusion of higher order PT terms in molecular parameters can improve the accuracy of calculated properties, especially for systems with strong anharmonicities. These terms can also provide insights into the anharmonicity of a molecule and its potential energy surface.

3. What methods are commonly used to calculate higher order PT terms?

The most commonly used methods for calculating higher order PT terms are perturbation theory (PT) and coupled-cluster theory (CC). These methods involve the calculation of higher order derivatives of the PES, which can be computationally demanding, but can be approximated using numerical differentiation techniques.

4. Are higher order PT terms important for all types of molecules?

No, the importance of higher order PT terms in molecular parameters depends on the anharmonicity of the molecule and the level of accuracy required for the calculation. For most small molecules, these terms can be neglected without significant loss of accuracy.

5. How can one determine if higher order PT terms are important for a particular molecule?

One way to determine the importance of higher order PT terms is to perform calculations with and without their inclusion and compare the results. If the difference in the calculated properties is significant, then the higher order PT terms should be included in the calculation.

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