Table 2.

Experimental mid-IR band positions recorded for Tr⁺ and calculated values using DFT (B3LYP/6-31G(d,p)) obtained in the present work (see Figure 1). Only the modes which are IR active are reported. Although they were computed in the C_2v symmetry point group, their symmetry in the point group of the molecular ion (D_7h) are listed.

Mode	Exp.	Ref.	Calc.
	ν	ν	ν (Inten.)	Sym.
νc	630	633,[15] 634,[16] 655[17]
ν4	652	658,[15] 660,[16] 685[17]	646(85.8)	A”2
ν8	994	992,[15] 992[16]	989(3.7)	E’1
ν14	1486	1477,[15] 1477[16]	1480(42.9)	E’1

Note: All frequencies in cm⁻¹, intensities in km · mol⁻¹. Scaling factor 0.974. ν_c is a combination band of the two lowest lying fundamental bands of Tr⁺. Cf. Fig. S16 – S18. in the SI for the visualisation of modes.