Experimental Determination of the Electric Dipole Moment of the Ground Electronic State of CH

Abstract

It seems likely that the 3400-Mc/sec transition between the lambda doublets of the lowest rotational state of CH in interstellar space will be soon observed. 1 ' 2 The absorption line intensity for such a transition depends upon the concentration of CH molecules, the state temperature, the transition frequency, and the square of the CH electric dipole moment. 3 We report here an experimental determination of the CH electric dipole moment.The electric dipole moment of CH was determined from simultaneous observation of Stark splittings in the J = i, 2 n i/2 states of CH and OH. The J = i, 2 n i/2 level splits into two components whose separation is, except for small corrections due to the finite lambda doubling, proportional to the applied electric field and the electric dipole moment. The transitions studied here were the P 12 (l) line of CH at 3890.22 A, arising from the transition C 2 S + -X 2 n i/2 , and the R 2 (l) line of OH at 3084.05 A, arising from the transition A 2 Z + *X 2 n i/2 . For these lines, second-order Stark effects in either the upper or lower states shift both first-order Stark components but do not affect the measured separation. 3 Electronically excited molecules were produced in a direct-current discharge tube containing methyl alcohol vapor and helium gas at a total pressure of 1 mm Hg. The discharge tube was constructed to provide electric fields up to 50 000 V/cm in the cathode dark space. 4The CH and OH emission lines were simultaneously observed at a dispersion of 4 cm""Vmm on a stigmatic grating spectrograph. Measured Stark splittings are listed in Table I. Figure 1 is a plot of the observed Stark splittings of CH corrected for lambda doubling against observed Stark splittings for OH similarly corrected. The corrections are small, approximately 2%. From a least-squares determination of the slope of the line through the origin we obtain the ratio of the electric dipole moments

Calculation of static molecular properties in the framework of the unitary group based coupled cluster approach

“…The total energies, dipole moments, and polarizabilities obtained with both the POLl and AN0 basis sets at the experimental geometries (35) using various methods are summarized in Table 3, and compared with the available experimental values (47)(48)(49)(50)(51)(52) in the case of dipole moments. These results enable us to draw a number of interesting conclusions concerning the role of the correlation effects, the use of relaxed (R) vs. nonrelaxed (N) orbitals, and the size of the basis set employed.…”

The far-infrared and microwave spectra of the CH radical in the v=1 level of the X2Π state

“…The intensity of a line in absorption can be obtained by multiplying the line strength by the square of the dipole moment for CH (1.40 D [38,39]), by the transition frequency and by the population difference between the lower and upper states. The Einstein A-coefficient for spontaneous emission from state i to j can also be calculated from the line strengths by use of the relation Table 7 is not quite complete because the transitions with D J = 1, F 2 ‹ F 1 have been omitted.…”

The far-infrared laser magnetic resonance spectrum of the 13CH radical

“…The intensity of the line in absorption can be obtained by multiplying the linestrength by the square of the dipole moment l (1.40 Debye for CH [36,37]), by the transition frequency and by the population difference between the lower and upper states. The Einstein A-coefficients for spontaneous emission from state i to j can also be calculated from the linestrengths by use of the relation Table 6 is not quite complete because the transitions with DJ ¼ 1, F 2 F 1 have been omitted.…”