CH3CCH, ν9
Propyne, methylacetylene, ν9 (δCCH)
Species tag 040508
Date of EntryMay 2005
ContributorH. S. P. Müller

The observed rovibrational and rotational transition frequencies have been described in
(1) H. S. P. Müller, P. Pracna, and V.-M. Horneman, 2002, J. Mol. Spectrosc. 216, 397, in
(2) P. Pracna, H. S. P. Müller, S. Klee, and V.-M. Horneman, 2004, Mol. Phys. 102, 1555, and in references therein.
The ν9 band is the second lowest and the strongest fundamental in propyne. The ν9 band is a doubly degenerate vibration. State number 1 describes k values ≤ 0, while state number 2 indicates states with k > 0.
The data have been subjected to a combined fit consisting of v10 = 0, 1, 2 and v9 = 1 pure rotational data as well as ν10, ν9, and 2ν10 – ν10 rovibrational data. A strong, isolated line has an estimated precision of 0.0002 cm–1; the accuracies are probably slightly worse because of calibration uncertainties.
The Coriolis interactions of v9 = 1 with v10 = 1 and the Fermi interaction with v10 = 2 described in (1) and (2), have been taken into account. The latter occurs at K = 1 between l = –1 of v9 = 1 and l = +2 of v10 = 2, causing non-zero intensity in some transitions of 2ν10; these transitions have the upper state number 3. Its interactions with states of the next higher polyad have not been taken into account in this prediction and the Coriolis interaction with v10 = 2 at higher K have not been considered in the current model. Therefore, predictions for transitions with k ≤ –10 or k ≥ 13 should be viewed with caution.
The transition dipole moment has been derived from intensity measurements of individual rovibrational transitions by
(3) G. Blanquet, J. Walrand, and M. Dang-Nhu. 1992, Spectrochim. Acta, 48A, 1231.
Besides the ground vibrational state, the partition function takes into account the states v10 = 1, v9 = 1, and v10 = 2. Their respective contributions are given in parentheses as long as they are different from 0 within the quoted digits.

Lines Listed5974
Frequency / GHz< 20395
Max. J86
log STR0-100.0
log STR1-8.5
Isotope Corr.-0.0
Egy / (cm–1)0.0 / 638.58
 µa / D 
 µb / D0.222
 µc / D 
 A159140. / 159100.
 B8545.877 / 8551.062
 C = B
 Q(300.0)17826.0720 (4518.3010; 1040.8925, 1412.0356)
 Q(225.0)9357.5685 (1740.3447; 245.6071, 322.7121)
 Q(150.0)4209.3392 (333.2663; 17.6501; 21.7571)
 Q(75.00)1362.3596 (5.1339; 0.0144; 0.0146)
 Q(37.50)481.7197 (0.0035)
detected in ISM/CSMno

Database maintained by Holger S. P. Müller and Sven Thorwirth, programming by D. Roth and F. Schloeder