Table 1
Spectroscopic parameters of ![Mathematical equation: $\[\mathrm{CH}_{3}^{+}\]$](/articles/aa/full_html/2026/07/aa60397-26/aa60397-26-eq20.png)
in the ground vibrational state and the ν2/ν4 dyad.
| Parameter | Changala et al. a | This workb |
|---|---|---|
| v = 0 | ||
| B | 9.36123(15) | 9.36175(10) |
| C | 4.615768(49) | 4.5942(14) |
| DJ × 103 | 0.7263(17) | 0.7344(10) |
| DJK × 103 | −1.3072(25) | −1.310(2) |
| DK × 103 | 0.6296(44) | 0.5276(9) |
| HJ × 109 | −0.189(63) | ... |
| ν2 = 1 | ||
| ν2 | 1405.743(58) | 1405.8099(11) |
| B | 9.3489(28) | 9.3459(4) |
| C | 4.6340(19) | 4.630(9) |
| DJ × 103 | 0.398(28) | 0.73(3) |
| DJK × 103 | −0.720(53) | −1.36(6) |
| DK × 103 | 0.375(33) | 0.57(7) |
| ν4 = 1 | ||
| ν4 | 1395.238(39) | 1395.2471(15) |
| B | 9.4488(22) | 9.441(6) |
| C | 4.57126(76) | 4.557(4) |
| ζ4 | −0.10295(44) | −0.1114(3) |
| ηJ,4 × 103 | ... | 6.1(55) |
| ηK,4 × 103 | ... | −6.5(55) |
| DJ × 103 | 0.809(24) | 0.792(14) |
| DJK × 103 | −1.370(46) | −1.44(4) |
| DK × 103 | 0.616(25) | 0.59(3) |
| v2/ν4 | ||
| Fab | −8.9070(21) | −8.947(2) |
| Fab,c | 0.02232(20) | 0.0227(9) |
| Fab,J × 103 | ... | 1.73(3) |
| Fab,K × 103 | ... | −2.8(13) |
| Fit rms | 0.064 | 0.0063 |
Notes. All values are in cm−1 (wavenumber) except that of ζ4, which is dimensionless. Parameters for ν3 are reported in Table D.1. (a)Values based on initially ab initio computed spectroscopic parameters, later refined by fitting to JWST MIRI data. See Changala et al. (2023) for details. (b)Global Fit of ν2/ν4 dyad and ν3 data measured by Jagod et al. (1994). Errors on parameters (values in parentheses) are equal to 1σ.
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