Zeeman Effect in the Electronic Spectrum of Solid CS2

Abstract

The lowest‐energy ${}^3{A}_2{\mathrm{\hspace{0.17em}\leftarrow \hspace{0.17em}}}^1{\Sigma }_g^{+}$ singlet‐triplet transition of CS₂ has been studied in the CS₂ crystal at 4.2°K. The spectrum consists mainly of progressions in the bending mode ${\nu }_2\prime$ . The following values for the upper state frequencies have been obtained ${\mathrm{(\nu }}_1\text{′\hspace{0.17em}=\hspace{0.17em}677}{\mathrm{cm}}^{\text{−1}}{\mathrm{,\; \nu }}_2\text{′=309}{\mathrm{cm}}^{\text{−1}})$ and the unobserved $B_2$ electronic origin has been calculated to be at 24 739 cm⁻¹. Zeeman studies of the 3676‐Å band system have been used to assign a very weak component of a vibronic band of this system as a crystal field induced transition to the ${\mathrm{(A}}_1{\mathrm{,\; B}}_1)$ pair of spin sublevels of the triplet state ${}^3{A}_2$ . The zero field splitting (ZFS) parameter of 36 ± 1 cm⁻¹ thus obtained for the vibronic state is comparable with the one calculated by Hougen [J. Chem. Phys. 41, 363, (1964)] from Zeeman line broadening experiments in the gas phase done by Douglas and Milton [J. Chem. Phys. 41, 357 (1964)] on comparable vibronic bands. The large value of the ZFS parameter can be explained if it is assumed that the ${}^3{A}_2$ and ${}^3{B}_2$ states are quite nearby.