D. Boucher

Microwave spectra of molecules of astrophysical interest. XIX. methyl cyanide

The microwave spectrum of methyl cyanide is critically reviewed for information applicable to radio‐astronomy. Molecular data such as the derived rotational constants, centrifugal distortion parameters, hyperfine coupling constants, electric dipole moment and molecular structure are tabulated. The observed rotational transitions are presented for the astronomically interesting isotopic forms and the lowest lying vibrational state of methyl cyanide. Calculated rotational transitions are presented for the ground vibrational state of 12CH312C14N, 13CH312C14N, 12CH313C14N, 12CH312C15N, and for the vibrationally excited state ν8 of 12CH312C14N.

Microwave spectra, centrifugal distortion constants, and rz structure of acetonitrile and its isotopic species

Abstract The ground-state microwave spectra of acetonitrile and acetonitrile-d3 and their 13C and 15N isotopic species have been remeasured between 8 and 240 GHz. The derived quartic centrifugal distorition constants are in very good agreement with the values calculated from the general harmonic force field. The rotational constants we have obtained allow us to calculate very accurate rs and rz structures. The rz structure is: r(CC), 1.4617 (6) A; r(CN), 1.1567 (6) A; r(CH), 1.0947 (24) A; ∡(CCH), 109.85° (10). This structure shows no significant difference from the parameters derived in an earlier electron diffraction study.

The rotational constants of methyl lodide

Abstract The rotational spectra of CH 3 l ( v = 0; v 3 = 1; v 3 = 2; v 6 = 1), 13 CH 3 l ( v = 0), and CD 3 l ( v = 0) were observed in the submillimeter-wave region. These data have been combined with the microwave and millimeter-wave measurements to determine with high accuracy the rotational and centrifugal distortion constants. An overall fit including rotational data and infrared laser measurements yields a set of molecular parameters for the ν 6 band of CH 3 l.

Microwave spectra of propyne and its [13C] isotopic species: Refined molecular structure of propyne

Abstract The ground state microwave spectrum of propyne is remeasured between 60 and 240 GHz with a molecular beam spectrometer. These high resolution measurements allows us to accurately determine the rotational constant and all the determinable quartic and sextic centrifugal distortion constants: B = 8 545 877.12 (12) kHz; DJ = 2.9423 (13) kHz; DJK = 163.423 (20) kHz; HJ = 0.0097 (40) Hz; HJK = 0.935 (136) Hz; and HKJ = 5.23 (27) Hz (95% confidence limits are shown in parentheses). The spectra of the [13C]isotopic species are also reinvestigated between 30 and 240 GHz with a video spectrometer. With the accurate rotational constants we derive from those spectra a new r8 structure is calculated for the CC bond lengths: r 8 ( CC ) = 1.4586 (2) A and r 8 ( CC ) = 1.2066 (2) A .

High-resolution rotational spectrum of methyl cyanide

Abstract The ground-state microwave spectrum of methyl cyanide is remeasured between 70 and 240 GHz with a molecular beam spectrometer and by use of the Lamb dip method. It allows us to determine with great accuracy the B rotational constant, the quartic and sextic centrifugal distortion constants, the nuclear quadrupole coupling constant, and the spin-rotation constants of nitrogen. The magnetic shielding constants of nitrogen are also determined.

High resolution millimeter‐wave spectrum of methyl bromide. Spin–rotation and nuclear shielding tensors of bromine

The ground state rotational spectrum of CH3 Br has been observed using a molecular beam‐absorption spectrometer. The B rotational constant and the quartic and sextic centrifugal distortion constants are determined with great accuracy. From the hyperfine splitting the quadrupole coupling constant and the spin–rotation constants of the two isotopic species 79Br and 81Br can also be deduced. These data are used to determine the elements of the bromine nuclear magnetic shielding tensor.

Doppler-free rotational spectrum of methyl iodide. Nuclear quadrupole, spin-rotation and nuclear shielding tensors of iodine

Abstract The ground-state microwave spectrum of methyl iodide has been measured between 59 and 240 GHz with a molecular beam spectrometer and by use of the Lamb dip method. The following molecular parameters have been accurately determined: B = 7501275.70(2) kHz; D J = 6.3070(2) kHz; D JK = 98.762(3) kHz; H J = −0.0051(6) Hz; H JK = 0.04(2) Hz; H KJ 4.51(3) Hz; eq. Q = −1934.136 (5) MHz; C ⊥ = −17.40(6) kHz; C | = −19.4(5) kHz; x J = −1.41(4) kHz; x K = −38(1) kHz and x d = 26.2(6) kHz. The last three constants characterize the interaction of centrifugal distortion with quadrupole coupling. The data are used to determine the elements of the iodine nuclear magnetic shielding tensor. Comparisons of the shielding are made for molecules which contain one iodine atom.

The high resolution rotational spectrum of methyl chloride. The spin—rotation and nuclear magnetic shielding tensors

Abstract A high resolution study of the rotational spectrum of CH 3 35 Cl in the vibrational ground state has been performed using a molecular beam spectrometer. By fitting the measured transitions to an appropriate molecular hamiltonian the values of the following molecular parameters have been obtained: B = 13 292.8763 MHz; D J = 18.089 kHz; D JK = 198.76 kHz; H KJ = 9 Hz; eqQ = −74.750 MHz; C ⊥ = −2.7 kHz and C ∥ = −7 kHz. These data are used to determine the paramagnetic contribution to the chlorine nuclear magnetic shielding tensor. The diamagnetic contribution is also calculated using a semi-empirical method. Comparisons of the average shieldings are made for related molecules.

Microwave spectra of methyl chloride, methyl bromide, and methyl iodide in the ν6 = 1 excited vibrational state

Abstract The rotational spectra of CH 3 35 Cl, CH 3 37 Cl, CH 3 79 Br, CH 3 81 Br, and CH 3 I in the ν 6 state were observed between 8 and 240 GHz. For CH 3 Br and CH 3 I, the present data were combined with the pure quadrupole resonances of Oka et al. to determine the molecular constants. Our measurements have enabled us to notably improve the molecular constants for the ν 6 excited states.

The high resolution rotational spectrum of methyl iodide using a molecular beam spectrometer

The hyperfine structure of the J = 5 ← 4 transition of the ground-state rotational spectrum of methyl iodide is investigated with a molecular beam-absorption spectrometer. Combining these measurements with the results of conventional spectroscopy allows us to determine with great accuracy the B rotational constant, some of the quartic and sextic centrifugal distortion constants, the two spin-rotation constants of iodine and the quadrupole coupling constant. Moreover, it is found necessary to take into account the interaction of centrifugal distortion with quadrupole coupling.