Multi-channel distorted-wave Born approximation for rovibrational transition rates in molecular collisions
Taha Selim1, Arthur Christianen1, Ad van der Avoird1
1Theoretical Chemistry Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
The Journal of Chemical Physics
|July 23, 2021
Summary
Calculating molecular transition rates for interstellar environments is crucial. A new computational method for CO2-He collisions proves efficient and accurate, outperforming older approximations for modeling protoplanetary disks.
Area of Science:
- * Astrochemistry and Computational Physics.
- * Molecular Collisions and Interstellar Medium Physics.
Background:
- * Accurate modeling of protoplanetary disks and interstellar media requires rovibrational transition rate coefficients.
- * Collisions with helium (He) and hydrogen (H) are key for molecules like carbon dioxide (CO2).
Purpose of the Study:
- * To develop and validate an efficient computational method for calculating state-to-state rate coefficients.
- * To apply this method to CO2-He collisions, crucial for astrophysical modeling.
- * To assess the accuracy of different computational approaches.
Main Methods:
- * Utilized the coupled-channel (CC) method for rotational transitions.
- * Employed the multi-channel distorted-wave Born approximation (MC-DWBA) for vibrational transitions.
- * Computed new ab initio three-dimensional potential energy surfaces for CO2-He.
Main Results:
- * The MC-DWBA method provides results nearly as accurate as full CC calculations but is more computationally efficient.
- * Calculations were performed for CO2 distorted along symmetric (ν1) and asymmetric (ν3) stretch coordinates.
- * The vibrational coupled-channel rotational infinite-order sudden method was found to significantly underestimate cross sections and rate coefficients.
Conclusions:
- * The developed MC-DWBA method is a reliable and efficient tool for calculating rovibrational transition rates in CO2-He collisions.
- * This method advances the accurate modeling of interstellar environments and protoplanetary disks.
- * Findings highlight the limitations of the infinite-order sudden approximation for these systems.
More Related Videos
Related Concept Videos
01:16IR Spectroscopy: Hooke's Law Approximation of Molecular Vibration
2.1K
A covalently bonded heteronuclear diatomic molecule can be modeled as two vibrating masses connected by a spring. The vibrational frequency of the bond can be expressed using an equation derived from Hooke's law, which describes how the force applied to stretch or compress a spring is proportional to the displacement of the spring. In this case, the atoms behave like masses, and the bond acts like a spring.
According to Hooke's law, the vibrational frequency is directly proportional to...
According to Hooke's law, the vibrational frequency is directly proportional to...
2.1K
01:02¹H NMR: Interpreting Distorted and Overlapping Signals
1.2K
Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
1.2K
01:16UV–Vis Spectroscopy: Molecular Electronic Transitions
2.0K
In Ultraviolet–Visible (UV–Vis) spectroscopy, the absorption of electromagnetic radiation is used to probe the electronic structure of molecules. This technique provides insights into molecular electronic transitions, particularly the movement of electrons between different molecular orbitals. Radiation is absorbed if the energy of the electromagnetic radiation passing through the molecule is precisely equal to the energy difference between the excited and ground states. During this...
2.0K
01:27Distribution of Molecular Speeds
4.3K
The motion of molecules in a gas is random in magnitude and direction for individual molecules, but a gas of many molecules has a predictable distribution of molecular speeds. This predictable distribution of molecular speeds is known as the Maxwell-Boltzmann distribution. The distribution of molecular speeds in liquids is comparable to that of gases but not identical and can help to understand the phenomenon of the boiling and vapor pressure of a liquid. Consider that a molecule requires a...
4.3K
00:52¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
966
At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
966
01:08Spin–Spin Coupling Constant: Overview
1.1K
In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must...
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must...
1.1K