L. H. Johnston

Laser-Stark spectrum of methyl alcohol at 890.761 GHz with the HCN laser

Abstract The laser-Stark spectrum of methanol has been studied up to Stark fields of about 55 kV/cm with the 890.761-GHz HCN laser, in both parallel and perpendicular polarizations. Extensive series of absorption lines have been assigned to the J = 6 to 15 members of the k = 6 ← 5 Q branch of the v = 0 E torsional state of CH3OH. Also, 21 M components of the Jk = 71 ← 62 A ± doublet in the v = 1 excited torsional state have been identified. Efforts to analyze the Q-branch spectra in terms of dipolar parameters and zero-field frequencies were hampered by very high statistical correlations in the least-squares fits. However, it proved necessary to permit the upper-state value of μa to exceed that of the lower state, by 0.0014 D, and to introduce J dependence of μa. Analysis of the Stark shifts of the excited torsional state transition yielded a μa of 0.93 D, about 0.04 D greater than the mean value for the ground state.

Submillimeter laser Stark spectroscopy of 14ND3

Abstract A submillimeter laser Stark spectrum of fully deuterated ammonia (14ND3) has been observed with the 195-μm and 195′-μm lines of the DCN laser. The spectra observed were identified as dipole forbidden a ← a and s ← s rotation-inversion transitions, the multiplet JK = 5K←4K in the ground vibrational state for K = 1, 2, 3, and 4. The forbidden zero-field rotation-inversion transition frequencies are given, and the K-dependent dipole-moment values are determined by virtue of the fact that the same transition could be observed at two different laser frequencies.

Submillimeter Laser Stark spectroscopy of methyl fluoride at 311 μm

Submillimeter Laser-Stark spectra have been observed for methyl fluoride using the 311 μm line of the HCN laser. The spectra were taken for both π and σ polarizations and up to 65,000 V/cm. We identify the multiplet transitions as JK=19K←18K in the ground vibrational state. We have seen seven families with K=10, 11, 12, 13, 14, 15, and 16. Zero field frequencies are given for all families and are more accurate than those calculated from Graners molecular constants. Second order Stark effect has been observed for the first time in a symmetric top molecule in the presence of a large first-order Stark effect.

Laser Stark spectroscopy of 1,1 difluoroethylene at λ=337 μm

Abstract Laser Stark spectra are given for 1,1 difluoroethylene (H 2 CCF 2 ) using laser λ = 337 μm. Three families of resonances are analyzed, two of them being the related transitions J ( K a , K c ) = 47(40, 8) ← 46(40, 7) and 47(40, 7) ← 46(40, 6). Relationships between the two transitions permit the calculation of both the zero-field transition frequencies and the effective dipole moment. A third family is assigned as 38(32, 7) ← 37(30, 8). The Stark shift is quasi-linear with E field, dominated by near-degenerate doublet interactions. Extended measurements and a reanalysis of the microwave spectrum are reported, in connection with the analysis of the far infrared spectrum.

Stark spectroscopy of CD3OD with the HCN laser

Abstract The laser Stark spectrum of fully deuterated methanol has been studied using the 337 and 311-μm lines of the HCN laser. Numerous families of absorption lines have been observed for both parallel and perpendicular polarizations up to 60 kV/cm. An extensive series of absorption lines observed at 311 μm has been assigned to the J = 11 to 19 members of the K = 11 ← 10 E2 Q branch in the vt = 0 ground torsional state of CD3OD. An R-branch transition observed at 311 μm has been identified as the JK = 117 ← 106A, vt = 0 transition. Three families of resonances observed at λ = 337 μm are identified as JK = 183 ← 172E1, vt = 0; JK = 173 ← 164E1, vt = 1; and JK = 97 ← 86A, vt = 0, transitions. Zero-field frequencies for all the assigned transitions are given with improved accuracy over those calculated from available molecular constants. For the Q-branch series, the branch origin and the series expansion coefficients are presented.

Laser stark spectroscopy of CD3OH and13CH3OH at 311μm

Laser Stark spectra have been observed for CD3OH and13CH3OH using the 311 μm line of the HCN laser. The spectra were taken for both parallel and perpendicular polarizations up to 60,000 Volts/cm. For CD3OH, the two characteristic structures in the spectra have been identified as the JK=144←133, A± doublet in the vt=0 torsional state. For13CH3OH, the low field structure observed is assigned as JK=153←142, A− in the vt=0 torsional state.

Submillimeter laser Stark spectroscopy of13CH3F with the 337 μm line of the HCN laser

Submillimeter laser-Stark spectra have been observed for the isotopic species of methyl fluoride,13CH3F, using the 337 μm line of the HCN laser. We have identified the multiplet transitions as JK=18K←17K in the ground vibrational state. Ten distinct families with K=8, 9, 10, 11, 12, 13, 14, 15, 16 and 17 have been observed. Zero-field frequencies for all the transitions are given and in most cases with better accuracy than predicted from the previous constants.

Laser-Stark spectrum of methyl alcohol at 311 μm

Laser-Stark spectra have been observed for methyl alcohol using the 311 μm line of the HCN laser. Partial assignments are presented for the three most distinctive structures in the spectra. The low field structure is clearly associated with a member of the J=20↭19qRa-type multiplet, and is tentatively identified as the k=13 A vt=0 transition. The other two structures originate from the 93↭82 E vt=0 transition, and from a member of the k= 6↭5 A vt=1 Q branch, tentatively assigned as the J=32 member.

Laser Stark spectroscopy of CD3Cl at λ=337μm

A submillimeter laser Stark spectrum has been observed for fully deuterated Methyl Chloride (CD3Cl) with the 337 μm line of the HCN laser up to Stark fields of about 54000 V/cm. The spectra were taken for both Parallel and Perpendicular Polarizations and the multiplet transitions were identified as JK=42K←41K in the ground vibrational state. Three families with K=12, 13 and 14 have been identified and their zero field frequencies have been given with improved accuracy over those calculated from available molecular constants.

Laser stark spectroscopy of SO2 with the HCN laser

The Far Infrared (FIR) laser Stark spectrum ofSO2 was investigated using the 337 μm line of the HCN laser. Two distinct families, one originating at low field and the other at high field, were observed. The high field transition is identified as theJK−1,K+1=225,17←214,18, v2=1 transition. A significant fourth-order Stark shift was observed for this transition in the presence of a large second-order Stark shift. The zero-field frequency of the assigned transition was obtained by accounting for the fourth-order contribution.