Near-Infrared High Resolution Diode Laser Spectrum of the CH2 &btilde;1B1 <-- &atilde;1A1 Transition

Area of Science:

• Physical Chemistry
• Molecular Spectroscopy
• Laser Instrumentation

Background:

• Transient absorption spectroscopy is crucial for studying short-lived molecular species.
• High sensitivity is required to detect weak spectral features of reactive intermediates like methylene.
• Understanding the electronic and bending potentials of small molecules like CH2 is fundamental in chemistry.

Purpose of the Study:

• To construct and characterize a novel diode laser-based spectrometer for gas-phase transient absorption measurements.
• To achieve high sensitivity for detecting previously unobserved molecular spectra.
• To investigate the rovibronic structure and bending potential of singlet methylene (CH2).

Main Methods:

• Development of a diode laser spectrometer operating near 1 µm.
• Implementation of a dual-beam detection system for noise cancellation.
• Measurement of transient absorption spectra of singlet methylene (CH2) in the 9780–10070 cm⁻¹ range.

Main Results:

• The spectrometer achieved a minimum detectable absorption of 1 x 10⁻⁴ in 0.5 µsec.
• Previously undetected rovibronic spectra of singlet methylene (CH2) were observed.
• Assignment of transitions involving low-lying Ka = 1 levels in the b̃ ¹B₁ state of CH2.

Conclusions:

• The new spectrometer is highly sensitive and effective for gas-phase transient absorption studies.
• The observed spectra provide new data on the lowest energy levels of singlet methylene in the b̃ ¹B₁ electronic state.
• These findings offer valuable insights into the bending potential energy surface of CH2, particularly near the conical intersection of its lowest singlet states.