High‐resolution, slit jet infrared spectroscopy of hydrocarbons: Quantum state specific mode mixing in CH stretch‐excited propyne

摘要: A direct absorption, difference frequency, infrared laser spectrometer with 10−4 cm−1 resolution combined slit supersonic jet optical pathlengths is presented as a tool for the study of mode–mode vibrational coupling in laser‐excited hydrocarbons. These weak couplings are evidenced our frequency domain studies by virtue transitions to isolated upper J states that split into multiplets under sub‐Doppler resolution. Instrument performance demonstrated investigating 3000–3300 C–H stretch fundamental region 12C3 propyne, well 12C213C propynes observed natural isotopic abundance. No appreciable state mixing ν1=1←0 and ν6=1←0 spectra at T=4 K. However, near‐resonant two‐state ν2 ν5+ν8+3ν10 ν2=1←0 transition propyne detected deperturbed provide an anharmonic matrix element 0.096 41(38) cm−1. This independent J’ thus arises from purely anharmoni...