Absorption and photoionization coefficients have been measured for H2CO in the 600–2000-Å region. Integrated oscillator strengths were determined for a number of strong Rydberg transitions above 1200 Å. From the photoionization curve the first adiabatic ionization potential was found to be 10.87±0.01 eV. As an aid in interpreting the absorption spectrum, theoretical calculations were made using a single-configuration self-consistent field procedure for the Rydberg states and a model which included mixing between the Rydberg and valence states. On this basis, weak absorption features between 1340 and 1430 Å have been assigned to the B11(σ → π *) valence state. The 1A1(π → π *) valence state is deduced to be strongly autoionized just above the 2B2 ionization limit.

The structural, spectroscopic, and thermochemical properties of three polyatomic molecules with internal rotation—HNO3(g), H2SO4(g), and H2O2(g)—have been reviewed. Three revised ideal gas thermodynamic tables result from this critical examination. The revisions involved the consideration of new spectroscopic information and the use of theoretical results to model the internal rotation in the H2SO4 molecule. Compared to previous calculations, the entropies at 298.15 K are unchanged for HNO3 and H2O2, but the high temperature values (T>4000 K) are significantly different. As for H2SO4, its thermodynamic functions differ significantly from values calculated earlier.

The ionization potentials of NO2 up to 28 eV have been measured using He i and He ii high-resolution photoelectron spectroscopy. The assignment of the ionized levels below 16 eV is straightforward, including the singlet–triplet splittings, and allows us to assign Rydberg series in the vacuum uv leading to the first five ionization potentials. Above 16 eV the spectrum is complicated by the absence of obvious singlet–triplet splittings. The assignments we propose fit in with a coherent scheme for the molecular-orbital energy levels of 16-, 17-, and 18-electron triatomic molecules. The SCF calculations have been performed on several states of NO2 and NO2+ (both open shell and closed shell) and the results are in quite good agreement with the experimental ionization potentials.

Self-consistent-field calculations are reported for the ground state of the water molecule in a contracted and uncontracted Gaussian basis set. The uncontracted set is shown to be near the Hartree–Fock limit for water. One-electron properties were computed from both wavefunctions. Our best estimates for several of these quantities are: dipole moment, μz = 1.995 D; quadrupole moment, θzz = − 0.108 and θxx = − 2.422 in buckinghams; octupole moment, Ωxxz = − 1.337 and Ωzzz = − 0.960 in units of 10−34 esu·cm3; average diamagnetic shielding at the proton, σAvd = 102.9 ppm; quadrupole coupling constant at the deuteron, (eqQ / h)AA = 343.9 kc/sec, and at the oxygen, (eqQ / h)aa = − 8.34 Mc / sec. The effect of including d-type Gaussian functions in the basis is examined.