# Collisional- and photo-excitations of Ca IV including strong 3.2 $\mu$m emission line

## TL;DR

This study uses advanced relativistic calculations to analyze electron-impact excitation of Ca IV, predicting a strong infrared emission line at 3.2 μm and providing detailed collision data relevant for astrophysical diagnostics.

## Contribution

First detailed relativistic R-Matrix study of Ca IV electron-impact excitation including extensive resonance analysis and collision strengths for 54 levels.

## Key findings

- Predicted strong 3.2 μm IR emission line in Ca IV.
- Collision strengths show extensive resonances and temperature dependence.
- Data includes all 1431 excitations among 54 levels.

## Abstract

We report a detailed study of features of electron-impact excitation (EIE) of Ca IV for the first time using the relativistic Breit-Pauli R-Matrix method with a large close coupling wavefunction expansion of 54 fine structure levels belonging to n=2,3,4 complexes. Our study predicts presence of a strong 3.2 $\mu$m emission line in IR. The EIE collision strength ($\Omega$) shows extensive resonances with enhanced background resulting in an effective collision strength ($\gamma$) of 2.2 at about 10,000 K that increases to 9.66 around 300,000 K. The present results include collision strength of all 1431 excitations among the 54 levels and effective collision strength for a limited number of transitions of possible interest. We have found extensive resonances in the low energy region, convergence of the resonances, and of the partial waves with the 54 levels wavefunction. At higher energy, the collision strength decreases beyond the resonance region for forbidden transitions, is almost constant or decreases slowly for dipole-allowed transitions with low oscillator strengths, and rises with Bethe-Coulomb behavior of ln(E)to almost a plateau for transitions with high f-values.