Millimeter-Wave Spectra of the CO Dimer: Three New States and Further Evidence of Distinct Isomers

The millimeter-wave spectrum of the normal isotope of the CO dimer, (¹²C¹⁶O)₂, has been systematically surveyed in the regions 75-105 and 131-174 GHz, with additional measurements covering the entire 60-176 GHz range. By combining these results and using the technique of combination differences based on previously known energy levels, 14 new rotational levels have been assigned and precisely (≈0.1 MHz) located. They belong to 3 completely new states, 1 with A⁺ symmetry and 2 with A⁻ symmetry. The position of the lowest energy A⁻ state results in a new and lower value for the effective tunneling splitting of the CO dimer, 3.73 cm⁻¹. The observation of dramatically different intensities for different bands supports the concept of two isomeric forms for (CO)₂, the ground state having a larger intermolecular separation (≈4.4 Å) with most likely a C-bonded configuration, and the low-lying (0.88 cm⁻¹) excited state having a smaller separation (≈4.0 Å) and an O-bonded geometry.     

Millimeter wave rotational spectrum of deuterofulminic acid,DCNO, in excited vibrational states

Rotational transitions of DCNO in the vibrational states 00002, 00003, 00020, and 00011 have been measured and analyzed. These results complete the presentation of assigned millimeter wave transitions of DCNO.The analysis of rotational l-type resonance in the 00002 and 00020 states is more satisfactory in the case of DCNO than in that of HCNO due to the absence of accidental resonances. The values obtained for the vibrational anharmonicity constant g₅₅ for 00002 and 00003 agree within experimental error with those found from the vibrational spectrum.An ambiguity in the assignment of the symmetry of the transitions in the four components of the 00011 vibrational state is discussed.     

A digitally controlled diode-laser spectrometer: Infrared spectrum of the ν4 band of acetonitrile between 890 and 960 cm−1

The ν₄ vibration-rotation spectrum of acetonitrile (CH₃CN) has been measured using a newly constructed diode-laser spectrometer controlled digitally by a microprocessor. The spectrum was observed in the range between 890 and 960 cm^?1 with Doppler-limited resolution. The P and R branches of the ν₄ fundamental band have been assigned up to K = 9. A small anomaly found in the high K lines is being explained by an anharmonic resonance with the v₈ = 3³ state. The determined interaction constant is small, but significant.     

The simulation of infrared bands from the analyses of rotational spectra: the 2ν9-ν9 and ν5-ν9 hot bands of HNO3

The results of millimeter and submillimeter wave rotational spectroscopy are used to simulate the complex structure of the 2ν₉-ν₉ and ν₅-ν₉ hot bands. The comparison data were obtained with a high-resolution Bruker FTIR. The combination of the quality of these data and the complexity of the spectra of these interacting states represents a stringent test for the simulation. It is shown that the agreement is very good and that this approach is generally advantageous. From this simulation, the ratios of the transition dipole moments for the 2ν₉-ν₉ and ν₅-ν₉ hot bands with respect to the ν₉ fundamental band were found to be 1.38(11) and 0.67(20), respectively. Using these results, the calculated integrated band intensities for the hot bands at were determined to be and . These results were used to successfully simulate high-resolution stratospheric spectra obtained from a balloon flight of the FIRS-2 spectrometer. The more general problem of the rotation-vibration database and the optimal use of both microwave and infrared data to define it is discussed. It is concluded that it is best if the combination of data takes place at the level of the original spectra.     

The CO dimer: new light on a mysterious molecule

The present state of research on the CO dimer is reviewed. In recent years, both infrared and millimeter-wave spectra have been measured and partially assigned by the use of combination differences. A microwave-millimeter wave double resonance experiment, reported here for the first time, provides independent confirmation of these assignments and the resulting (CO)₂ energy level scheme. In the double resonance experiment, the OROTRON spectrometer functions as a supersensitive intra-cavity millimeter-wave detector. We update the continuing, but difficult, experimental efforts in recording the spectra, the quest for secure assignments, and the construction of a consistent and reliable energy level scheme. Although at present we have only limited knowledge of some aspects of the CO dimer, such as its geometrical structure, we have succeeded in characterizing unambiguously nine “stacks” of ground state energy levels with “microwave accuracy” (∼0.1 MHz). Every energy level within a given stack exhibits the same symmetry: either A⁻ or A⁺. Only transitions between A⁺ and A⁻ levels are allowed, and consequently ordinary pure rotational transitions within a stack are forbidden. Transitions between stacks can be thought of as tunneling transitions, and the separation of the lowest energy A⁺ and A⁻ states corresponds to a value of for the effective “tunneling splitting” of the CO dimer. The stacks tend to fall into two groups, corresponding to “isomers” with effective inter-molecular separations of either 4.0 or 4.4 Å. The larger inter-molecular separation of the true ground state (4.4 Å) likely corresponds to a C-bonded configuration, while the low-lying excited state with the smaller separation (4.0 Å) likely displays an O-bonded geometry.     

Submillimeter-Wave Spectroscopy of Phosphaalkynes: HCCCP, NCCP, HCP, and DCP

The submillimeter-wave rotational spectra of the unstable phosphorus-bearing molecules HCCCP (phosphabutadiyne) and NCCP (C-cyanophosphaethyne) have been investigated in selected frequency regions between 490 and 815 GHz using the Cologne Terahertz Spectrometer. Both molecules were studied in their ground vibrational states. Additionally, vibrational satellites within the bending states v(4) = 1 and v(5) = 1 were recorded for NCCP. Furthermore, the ground state rotational spectra of the (13)C and (15)N isotopomers of NCCP were detected in natural abundance. The new measurements allowed us to evaluate the sextic centrifugal distortion constants for each isotopomer and vibrational state investigated. The pyrolysis reactions, through which HCCCP and NCCP were produced in situ, also yielded phosphaethyne, HCP, as a by-product. Some transitions of HCP and DCP were recorded in their ground vibrational states along with v(2) = 1 vibrational satellites of the former. Copyright 2001 Academic Press.     

The Millimeter- and Submillimeter-Wave Spectrum and the Dipole Moment of Ethylenimine

The 0(0)(0) bands of the ?(2)B(2)-&Xtilde;(2)A(1) and &Btilde;(2)B(1)-&Xtilde;(2)A(1) systems of SrNH(2) were observed at Doppler-limited resolution using a Broida oven source and laser-induced fluorescence detection. A full rotational analysis of both transitions was performed including K(a) levels up to 5 and J levels up to 55. The &Btilde;(2)B(1) state was found to be extensively perturbed and only some of the subbands could be analyzed. The ?(2)B(2) and &Btilde;(2)B(1) states undergo a strong Coriolis-type interaction which results in extremely large spin-rotation splittings in both states, effectively splitting all levels with K(a)(') not equal 0 into two well-separated spin components. Copyright 2000 Academic Press.     

Rotational spectrum of trans-trans diethyl ether in the ground and three excited vibrational states

We report the results of a comprehensive reinvestigation of the rotational spectrum of diethyl ether based on broadband millimetre-wave spectra recently recorded at The Ohio State University and in Warsaw, covering the frequency region 108-366 GHz. The data set for the ground vibrational state of trans-trans diethyl ether has been extended to over 2000 lines and improved spectroscopic constants have been determined. Rotational spectra in the first excited vibrational states of the three lowest vibrational modes of trans-trans-diethyl ether, ν₂₀, ν₃₉, and ν₁₂ have been assigned. The v₂₀ = 1 and v₃₉ = 1 states are near 100 cm⁻¹ in vibrational term value and are coupled by a strong c-axis Coriolis interaction, which gives rise to many spectacular manifestations in the rotational spectrum. All of these effects have been successfully fitted for a dataset comprising over 3000 transitions, leading to precise determination of the energy difference between these states, (ΔE/hc)=10.400222(5) cm⁻¹. A newly developed software package for assignment and analysis of broadband spectra is described and made available.     

Intermediate coupling model description of55Fe and57Fe

The properties of the negative parity states of⁵⁵Fe and⁵⁷Fe are investigated in the framework of the intermediate coupling model. In the model, a neutron or a quasineutron is coupled to anharmonic vibrations of the core. Anharmonicities of the vibrations are estimated through the observed properties of the core. Energy levels, spectroscopic factors and electromagnetic properties have been calculated. The results of the present calculations are also compared with available experimental results and other theoretical results. The model reasonably accounts for many of the properties of the low-lying states.