Permanent electric dipole moment and polarizability in Stark modulation spectra of the ICIB-X transition

Because the induced dipole moment due to polarizability in a moderate elect ric field is thought to be small, the Stark effect due to polarizability ha s generally been ignored for molecules that have a permanent electric dipol e moment. However, by observation of the Stark modulation spectra (SMS), we have confirmed that the effects of polarizability and of the permanent dip ole moment are sometimes comparable. Based on this observation, we have sou ght an estimate of the polarizability. It was also found that the effect of the polarizability on the SMS depends mainly on its isotropic part. Thus, for the B-X electric transition of the ICl molecule, the differences in iso tropic polarizabilities were estimated to be Delta<(alpha)over bar> = 3.4-3 .8 Angstrom(3) at the 3-1 transition, and Delta<(alpha)over bar> = 3.6-4.3 Angstrom(3) at the 1-0 transition, assuming that the differences of anisotr opic polarizability Delta alpha(an) are within the range 2-9 Angstrom(3) fo r both transitions. Thus, obtained values of Delta<(alpha)over bar> were co nfirmed to be in a reasonable range, in spite of a wide range uncertainty i n Delta alpha(an). (C) 1999 American Institute of Physics. [S0021-9606(99)0 0521-8].