Quantum chemical spectral characterization of CH2NH2+ for remote sensing of Titan's atmosphere

- The aminomethyl cation was detected in relatively high-abundance in Titan's upper atmosphere by Cassini.
- This cation is believed to play a role in the creation of HCNH+.
- Quantum chemical predictions indicate that CH2NH2+ may be responsible for lines observed in Titan's atmosphere from between 870 cm−1 and 900 cm−1.
- The other vibrational, rotational, and rovibrational spectra features are provided here for the first time.

Cassini has shown that CH2NH2+ is likely present in relatively high abundance in Titan's upper atmosphere. Relatively little is known about this molecule even though it contains the same number of electrons as ethylene, a molecule of significance to Titan's chemistry. Any studies on CH2NH2+ with application to Titan or its atmospheric chemistry will have to be done remotely at this point with the end of the fruitful Cassini mission. Consequently, trusted quantum chemical techniques are utilized here to produce the rotational, vibrational, and rovibrational spectroscopic constants for CH2NH2+ for the first time. The methodology produces a tightly fit potential energy surface here that is well-behaved indicating a strong credence in the accuracy for the produced values. Most notably, the 884.1 cm−1 NH2 out-of-plane bend is the brightest of the vibrational frequencies reported here for CH2NH2+, and an observed and unattributed feature in this spectral region has been documented but never assigned to a molecular carrier. Follow-up IR or radio observations making use of the 540 GHz to 660 GHz range with the 0.45 D molecular dipole moment will have to be undertaken in order to confirm this or any attribution, but the data provided in this work will greatly assist in any such studies related to CH2NH2+.