The electronic spectrum of chloroformic acid in comparison to formic acid.

The electronic spectra of chloroformic acid ClCOOH and formic acid HCOOH are computed in large-scale multireference configuration interaction (MRD-CI) calculations. The computed spectrum of formic acid is in reasonable agreement with prior calculations and experimental data. The first electronic transition of ClCOOH is computed at 6.41 eV (193.4 nm), about 0.5 eV higher than in HCOOH. Together with five strong transitions calculated at 7.66 eV (161.9 nm; 2(1)A' <-- X(1)A'), 8.36 eV (148.3 nm; 3(1)A' <-- X(1)A'), 8.49 eV (146.0 nm; 4(1)A' <-- X(1)A'), 9.00 eV (137.8 nm; 5(1)A' <-- X(1)A'), and 9.44 eV (131.3 nm; 7(1)A' <-- X(1)A'), this can serve as a guideline for experimental search of ClCOOH.