Infrared Frequency Comb Spectroscopy of CH2I2: Influence of Hot Bands and Pressure Broadening on the ν1 and ν6 Fundamental Transitions

Direct frequency comb spectroscopy was utilized to measure the vibrational absorption spectrum of diiodomethane, CH2I2, from 2960 to 3125 cm-1. The data was taken using a CH2I2 concentration of (6.8 {plus minus} 1.3) × 1015 molecule cm-3 and a total pressure of 10 - 300 mbar with either nitrogen or argon as the bath gas. The rovibrational spectra of two fundamental transitions, ν6 and ν1, were recorded and analysed. We suggest that a significant contribution to the observed congested spectra is due to population in excited vibrational states of the low energy ν4 I-C-I bend, resulting in transitions 6104nn and 1104nn where the integer n is the initial vibrational level v = 1 - 5. PGOPHER was used to fit the experimental spectrum, allowing for rotational constants and other spectral information to be reported. In addition, it was found that the peak widths for the observed transitions were limited by pressure broadening, resulting in a pressure broadening parameter of (0.143 {plus minus} 0.006) cm-1 atm-1 by N2 and (1.116 {plus minus} 0.006) cm-1 atm-1 by Ar. Further implications for other dihaloalkane infrared spectra are discussed.