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The experimental data for the deactivation of CO2(00°1) in CO2–CF2Cl2 and CO2–C4H4S mixtures are presented in the temperature range 323–463 K for different compositions. The relaxation rate per unit pressure (Pτ)−1 showed deviations from the linear mixture rule.

Proton spin-lattice relaxation times T1 were measured in mixtures of H2 with N2O as a function of density, composition, and temperature (200–400 K) in the region where [Formula: see text]. These data, along with the data obtained by Lalita and Bloom for H2–CO2, were interpreted, using Bloom–Oppenheim theory, to obtain the anisotropic intermoleeular potential parameters. Two models, (i) the Lennard–Jones (12–6) potential (LJP) and (ii) the modified Buckingham (exp-6) potential (MBP), were used to represent the isotropic part of the intermolecular potential. The relative anisotropy in the attractive r−6 term and the quadrupole moments of N2O and CO2 as obtained from MBP model are in better agreement with the values obtained from the polarizability data and the reported values, respectively, than those obtained from the LJP model.

Proton spin–lattice relaxation times have been measured in the gaseous mixtures CH4–N2 and CH4–CO2 as a function of density and composition in the temperature region 300–600 K. The values of T1/ρ extrapolated to 100% N2 and CO2 respectively were found to be proportional to T−n where n = 0.87 ± 0.14 for CH4–N2 and n = 0.91 ± 0.10 for CH4–CO2. It is not possible to fit these data using a hard sphere potential for the isotropic part. Using the Bloom–Oppenheim theory and assuming that the correlation time of the spin–rotation interaction can be approximated by the average lifetime of a molecule in the given J state, it is shown that the above temperature dependence can be fitted by a 12–6 Lennard–Jones potential combined with an appropriate anisotropic potential. We have obtained the strengths of the repulsive and attractive terms in the anisotropic potential by a least squares fit of the data. Using the known values of the quadrupole moments of N2 and CO2, the octopole moment of CH4 has been obtained.

Proton spin-lattice relaxation times, T1, have been measured in H2–Ar and H2–N2 gas mixtures as a function of density (10 1 data obtained by Foster and Rugheimer and by Williams in these mixtures below 300 K have been analysed using the Bloom–Oppenheim theory. Models for intermolecular potentials to explain the T1 data have been proposed. It is found that the relative anisotropy in the attractive part of the intermolecular potential which fits the T1 data best compares well with that evaluated using polarizability data.

Proton spin‐lattice relaxation times were measured in C2H4 and mixtures of C2H4 with He, A, and N2 as a fuction of density, composition, and temperature (300–600 K) in the region where T1∝ρ using a 30 MHz spin‐echo spectrometer. The values of T1/ρ for infinite dilution of C2H4, (T1/ρ)C2H4–X were found to be proportional to T−n, where n=1.43 for C2H4–C2H4, 0.54 for C2H4–He, 1.18 for C2H4–A, and 1.25 for C2H4–N2. These data were analyzed, using Bloom–Oppenheim theory and assuming that the correlation time of the spin−rotation interaction in a J state is equal to the lifetime of a molecule in that J state, to obtain information on the spin‐rotation coupling constant, up to a constant, as well as the intermolecular anisotropic interactions responsible for spin‐lattice relaxation in these systems.

The proton spin—lattice relaxation time T 1 was measured as a function of density in gaseous methyl chloride in the vicinity of T 1 minimum at 298 K. The experimental data were interpreted to obtain the effective value of the spin—rotation interaction constant for proton spins and the effective cross section for molecular reorientation.

The dependence of the proton T 1 in dilute CH 4 gas on temperature at constant density is appreciably different than for CH 4 in helium gas. This difference can give information on the CH 4 - CH 4 and CH 4 - He intermolecular potentials.

Rate constants for the transfer of energy from CO2(00°1) to ethane and n‐butane were measured using the laser induced fluorescence technique. The large magnitudes and the negative temperature dependence of the energy transfer rates indicate that near‐resonant energy transfer processes caused by long range forces are responsible for the deactivation of the asymmetric stretching mode of CO2. It is shown that the combination bands in the alkanes are likely to receive the energy from CO2(00°1). Using Sharma–Brau theory with Tam’s modification and our experimental results, the square of the transition dipole matrix elements of ν3+ν6 and ν9+ν11 bands of ethane are estimated. At any given temperature in the range 300–730 °K, the energy transfer cross section was found to increase linearly with n of CnH2n+2. It is suggested that the absorption intensity of the combination bands of the alkanes also increases linearly with n in the spectral range 2300–2400 cm−1.